[clang] Preferred name not generated nor used to declare variables in DWARF when used as template argument in code

# Problem

**TL;DR** Compiling the following code generates an object file whose DWARF doesn't contain the preferred name. This is true when compiling with `-ggdb` and with `-glldb`. Inspecting the DWARF shows that the variable is declared as `Foo >`. The preferred name, i.e. `BarInt` (case sensitive), is no where to be found in the DWARF.

Code:
```
template struct Foo;

typedef Foo BarInt;

template
struct [[clang::preferred_name(BarInt)]] Foo{};

int main() {
// BarInt barInt;
Foo fooBarInt;
return 0;
}
```

DWARF:
```
0x00000033: DW_TAG_variable
DW_AT_location (DW_OP_fbreg +11)
DW_AT_name ("fooBarInt")
DW_AT_decl_file ("/Users/royshi/demo/preferred_name/two.cpp")
DW_AT_decl_line (10)
DW_AT_type (0x00000043 "Foo >")
```

So lldb cannot print the preferred name:
```
(lldb) p fooBarInt
(Foo >) {}
```

## Repro

Use the above source code (call it `two.cpp`), then:
```
~/public_llvm/build/bin/clang -O0 -glldb -c two.cpp # or -ggdb

dwarfdump two.o

# Note: For me, the above clang cannot link, so I used xcrun clang++. It shouldn't matter which one you use.
xcrun clang++ two.o

lldb a.out -o "b two.cpp:10" -o "r" -o "p fooBarInt"
```

See compilation, dwarfdump, and lldb output:
- `-ggdb`: https://gist.github.com/royitaqi/cbf7a4d038f5b73dc60e5932bb2b593d
- `-glldb`: https://gist.github.com/royitaqi/46af47f0472976eb94b9725c073668df

I tested these on macOS. Haven't tested on Linux.

Note: If we uncomment that line `// BarInt barInt;`, the preferred name will be generated for `barInt` (type = `BarInt`), but not for `fooBarInt` (type = `Foo >`; I'm expecting `Foo`, since the type `BarInt` now exists).

--

cc @Michael137 , @clayborg

Start with the two.cpp reproducer and compile it using clang with -O0 -glldb and -ggdb. Inspect the generated DWARF and compare the variable's DW_AT_type with the expected preferred name, then use the shown LLDB command to verify that fooBarInt displays the preferred template spelling.

Written by the indexing model from the issue text.