[clang-check][syntax] Crash in shrinkToFitList: Assertion `(BeginChildren == Trees.end() || BeginChildren->first == Range.begin()) && "Range crosses boundaries of existing subtrees"' `failed.

This input is generated by a fuzzer.
Likely related to https://github.com/llvm/llvm-project/issues/207641.

```cxx
int foo = bar((struct {int a;}) );
```

```
clang-check --tokens-dump example.cpp -- -xc++ -std=c++23
```

```
clang-check: /home/ubuntu2404/llvm-project-196067/clang/lib/Tooling/Syntax/BuildTree.cpp:598: llvm::ArrayRef clang::syntax::TreeBuilder::Forest::shrinkToFitList(llvm::ArrayRef): Assertion `(BeginChildren == Trees.end() || BeginChildren->first == Range.begin()) && "Range crosses boundaries of existing subtrees"' failed.
#0 0x0000622a5c5e71f1 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/ubuntu2404/build-196067-assert/bin/clang-check+0x96d1f1)
#1 0x0000622a5c5e3dac llvm::sys::RunSignalHandlers() (/home/ubuntu2404/build-196067-assert/bin/clang-check+0x969dac)
#2 0x0000622a5c5e3f0c SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
#3 0x00007cc810a45330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
#4 0x00007cc810a9eb2c __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
#5 0x00007cc810a9eb2c __pthread_kill_internal ./nptl/pthread_kill.c:78:10
#6 0x00007cc810a9eb2c pthread_kill ./nptl/pthread_kill.c:89:10
#7 0x00007cc810a4527e raise ./signal/../sysdeps/posix/raise.c:27:6
#8 0x00007cc810a288ff abort ./stdlib/abort.c:81:7
#9 0x00007cc810a2881b _nl_load_domain ./intl/loadmsgcat.c:1177:9
#10 0x00007cc810a3b517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
#11 0x0000622a5c982e7f (/home/ubuntu2404/build-196067-assert/bin/clang-check+0xd08e7f)
#12 0x0000622a5c986aea clang::RecursiveASTVisitor<(anonymous namespace)::BuildTreeVisitor>::TraverseDeclContextHelper(clang::DeclContext*) BuildTree.cpp:0:0
#13 0x0000622a5c99c95d clang::RecursiveASTVisitor<(anonymous namespace)::BuildTreeVisitor>::TraverseCXXRecordDecl(clang::CXXRecordDecl*) BuildTree.cpp:0:0
#14 0x0000622a5c986aea clang::RecursiveASTVisitor<(anonymous namespace)::BuildTreeVisitor>::TraverseDeclContextHelper(clang::DeclContext*) BuildTree.cpp:0:0
#15 0x0000622a5c99f83b clang::RecursiveASTVisitor<(anonymous namespace)::BuildTreeVisitor>::TraverseTranslationUnitDecl(clang::TranslationUnitDecl*) BuildTree.cpp:0:0
#16 0x0000622a5c986439 clang::syntax::buildSyntaxTree(clang::syntax::Arena&, clang::syntax::TokenBufferTokenManager&, clang::ASTContext&) (/home/ubuntu2404/build-196067-assert/bin/clang-check+0xd0c439)
#17 0x0000622a5c07a4af (anonymous namespace)::DumpSyntaxTree::CreateASTConsumer(clang::CompilerInstance&, llvm::StringRef)::Consumer::HandleTranslationUnit(clang::ASTContext&) ClangCheck.cpp:0:0
#18 0x0000622a5deb0f9c clang::ParseAST(clang::Sema&, bool, bool) (/home/ubuntu2404/build-196067-assert/bin/clang-check+0x2236f9c)
#19 0x0000622a5c63e271 clang::FrontendAction::Execute() (/home/ubuntu2404/build-196067-assert/bin/clang-check+0x9c4271)
#20 0x0000622a5c68a308 clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/home/ubuntu2404/build-196067-assert/bin/clang-check+0xa10308)
#21 0x0000622a5c966cb7 clang::tooling::FrontendActionFactory::runInvocation(std::shared_ptr, clang::FileManager*, std::shared_ptr, clang::DiagnosticConsumer*) (/home/ubuntu2404/build-196067-assert/bin/clang-check+0xceccb7)
#22 0x0000622a5c960b2a clang::tooling::ToolInvocation::runInvocation(char const*, clang::driver::Compilation*, std::shared_ptr, std::shared_ptr) (/home/ubuntu2404/build-196067-assert/bin/clang-check+0xce6b2a)
#23 0x0000622a5c9631e2 clang::tooling::ToolInvocation::run() (/home/ubuntu2404/build-196067-assert/bin/clang-check+0xce91e2)
#24 0x0000622a5c964e19 clang::tooling::ClangTool::run(clang::tooling::ToolAction*) (/home/ubuntu2404/build-196067-assert/bin/clang-check+0xceae19)
#25 0x0000622a5bfff405 main (/home/ubuntu2404/build-196067-assert/bin/clang-check+0x385405)
#26 0x00007cc810a2a1ca __libc_start_call_main ./csu/../sysdeps/nptl/libc_start_call_main.h:74:3
#27 0x00007cc810a2a28b call_init ./csu/../csu/libc-start.c:128:20
#28 0x00007cc810a2a28b __libc_start_main ./csu/../csu/libc-start.c:347:5
#29 0x0000622a5c079045 _start (/home/ubuntu2404/build-196067-assert/bin/clang-check+0x3ff045)
Aborted (core dumped)
```

Start at clang/lib/Tooling/Syntax/BuildTree.cpp:598, especially Forest::shrinkToFitList and the BuildTreeVisitor path shown in the stack trace. Reproduce the crash with the supplied example.cpp and clang-check --tokens-dump command, then trace why this input crosses existing subtree boundaries. Done means clang-check no longer aborts on this reproducer.

Written by the indexing model from the issue text.