[clang] Assertion `!NewT.isNull()' failed.

Reproducer:
https://godbolt.org/z/TeYWYhq57
```cpp
template struct S {};
template using A = S;

A foo{42};
```

Backtrace:
```console
clang++: /root/llvm-project/llvm/tools/clang/lib/Sema/SemaTemplateDeductionGuide.cpp:373: clang::NonTypeTemplateParmDecl* {anonymous}::transformTemplateParam(clang::Sema&, clang::DeclContext*, clang::NonTypeTemplateParmDecl*, unsigned int, unsigned int, clang::MultiLevelTemplateArgumentList&): Assertion `!NewT.isNull()' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and dumped files.
Stack dump:
0. Program arguments: /opt/compiler-explorer/clang-assertions-trunk/bin/clang++ -g -o /app/output.s -mllvm --x86-asm-syntax=intel -fno-verbose-asm -S --gcc-toolchain=/opt/compiler-explorer/gcc-snapshot -fcolor-diagnostics -fno-crash-diagnostics -std=c++20
1. :4:10: current parser token ';'
#0 0x00000000043a2c48 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43a2c48)
#1 0x000000000439fb64 llvm::sys::RunSignalHandlers() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x439fb64)
#2 0x00000000043a0184 llvm::sys::CleanupOnSignal(unsigned long) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x43a0184)
#3 0x00000000042df218 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
#4 0x0000769d9ba45330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
#5 0x0000769d9ba9eb2c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9eb2c)
#6 0x0000769d9ba4527e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4527e)
#7 0x0000769d9ba288ff abort (/lib/x86_64-linux-gnu/libc.so.6+0x288ff)
#8 0x0000769d9ba2881b (/lib/x86_64-linux-gnu/libc.so.6+0x2881b)
#9 0x0000769d9ba3b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#10 0x0000000007786222 (anonymous namespace)::transformTemplateParam(clang::Sema&, clang::DeclContext*, clang::NonTypeTemplateParmDecl*, unsigned int, unsigned int, clang::MultiLevelTemplateArgumentList&) SemaTemplateDeductionGuide.cpp:0:0
#11 0x0000000007786d80 (anonymous namespace)::transformTemplateParameter(clang::Sema&, clang::DeclContext*, clang::NamedDecl*, clang::MultiLevelTemplateArgumentList&, unsigned int, unsigned int, bool) SemaTemplateDeductionGuide.cpp:0:0
#12 0x000000000778a618 (anonymous namespace)::BuildDeductionGuideForTypeAlias(clang::Sema&, clang::TypeAliasTemplateDecl*, clang::CXXDeductionGuideDecl*, clang::SourceLocation) SemaTemplateDeductionGuide.cpp:0:0
#13 0x00000000077d22a8 clang::Sema::DeclareImplicitDeductionGuides(clang::TemplateDecl*, clang::SourceLocation) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x77d22a8)
#14 0x00000000073bd91f LookupDirect(clang::Sema&, clang::LookupResult&, clang::DeclContext const*) SemaLookup.cpp:0:0
#15 0x00000000073bdbd2 clang::Sema::LookupQualifiedName(clang::LookupResult&, clang::DeclContext*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x73bdbd2)
#16 0x0000000007380a85 clang::Sema::DeduceTemplateSpecializationFromInitializer(clang::TypeSourceInfo*, clang::InitializedEntity const&, clang::InitializationKind const&, llvm::MutableArrayRef) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x7380a85)
#17 0x000000000704f60d clang::Sema::deduceVarTypeFromInitializer(clang::VarDecl*, clang::DeclarationName, clang::QualType, clang::TypeSourceInfo*, clang::SourceRange, bool, clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x704f60d)
#18 0x000000000705168d clang::Sema::DeduceVariableDeclarationType(clang::VarDecl*, bool, clang::Expr*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x705168d)
#19 0x00000000070854c8 clang::Sema::AddInitializerToDecl(clang::Decl*, clang::Expr*, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x70854c8)
#20 0x0000000006cc6cc4 clang::Parser::ParseDeclarationAfterDeclaratorAndAttributes(clang::Declarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6cc6cc4)
#21 0x0000000006ce6dc2 clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ce6dc2)
#22 0x0000000006c9244b clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c9244b)
#23 0x0000000006c92c4f clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c92c4f)
#24 0x0000000006c9f471 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c9f471)
#25 0x0000000006ca0385 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr&, clang::Sema::ModuleImportState&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6ca0385)
#26 0x0000000006c7d27a clang::ParseAST(clang::Sema&, bool, bool) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x6c7d27a)
#27 0x0000000004e930f8 clang::CodeGenAction::ExecuteAction() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4e930f8)
#28 0x00000000051bd7d8 clang::FrontendAction::Execute() (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x51bd7d8)
#29 0x000000000514b75d clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x514b75d)
#30 0x000000000529506d clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x529506d)
#31 0x0000000000d9f3fc cc1_main(llvm::ArrayRef, char const*, void*) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd9f3fc)
#32 0x0000000000d9600a ExecuteCC1Tool(llvm::SmallVectorImpl&, llvm::ToolContext const&, llvm::IntrusiveRefCntPtr) driver.cpp:0:0
#33 0x0000000000d9618d int llvm::function_ref&)>::callback_fn&)>(long, llvm::SmallVectorImpl&) driver.cpp:0:0
#34 0x0000000004f05f59 void llvm::function_ref::callback_fn>, std::__cxx11::basic_string, std::allocator>*, bool*) const::'lambda'()>(long) Job.cpp:0:0
#35 0x00000000042df654 llvm::CrashRecoveryContext::RunSafely(llvm::function_ref) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x42df654)
#36 0x0000000004f06a85 clang::driver::CC1Command::Execute(llvm::ArrayRef>, std::__cxx11::basic_string, std::allocator>*, bool*) const (.part.0) Job.cpp:0:0
#37 0x0000000004ec1b62 clang::driver::Compilation::ExecuteCommand(clang::driver::Command const&, clang::driver::Command const*&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ec1b62)
#38 0x0000000004ec2b7e clang::driver::Compilation::ExecuteJobs(clang::driver::JobList const&, llvm::SmallVectorImpl>&, bool) const (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ec2b7e)
#39 0x0000000004ececb5 clang::driver::Driver::ExecuteCompilation(clang::driver::Compilation&, llvm::SmallVectorImpl>&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0x4ececb5)
#40 0x0000000000d9b8ea clang_main(int, char**, llvm::ToolContext const&) (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd9b8ea)
#41 0x0000000000cb80fa main (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xcb80fa)
#42 0x0000769d9ba2a1ca (/lib/x86_64-linux-gnu/libc.so.6+0x2a1ca)
#43 0x0000769d9ba2a28b __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2a28b)
#44 0x0000000000d959b5 _start (/opt/compiler-explorer/clang-assertions-trunk/bin/clang+++0xd959b5)
clang++: error: clang frontend command failed due to signal (use -v to see invocation)
Compiler returned: 134
```

Reproduce the crash with the C++20 example and inspect transformTemplateParam in llvm/tools/clang/lib/Sema/SemaTemplateDeductionGuide.cpp, as identified by the assertion backtrace. Trace the deduction-guide construction for the type alias and verify that the reproducer no longer aborts on !NewT.isNull().

Written by the indexing model from the issue text.