[LLVM] [LLDB] [Native PDB] Add support for `lf_alias` for typedef types

[Walnut356]

Outlined here.

Local variables store their type via a type index, this is also true for global variables. Since typedef nodes don't live in the type stream, variables cannot have typedefs as types.

The front-end asks the TypeSystem about the type of a variable, but the TypeSystem and SymbolFile can't tell the difference between an unsigned char var; and a uint8_t var; because the actual type-node referenced by the variable will always be the underlying raw unsigned char node.

MSVC currently doesn't output lf_alias either, but it would solve some issues for C/C++ and third-party languages. lf_alias appears to be the equivalent of DW_TAG_typedef, so it would result in better feature parity with dwarf debug info.

[llvmbot]

@llvm/issue-subscribers-lldb

Author: Walnut (Walnut356)

Outlined [here](https://github.com//issues/114906#issuecomment-3152608683).

>Local variables store their type via a type index, this is also true for global variables. Since typedef nodes don't live in the type stream, variables cannot have typedefs as types. <br/><br/>The front-end asks the TypeSystem about the type of a variable, but the TypeSystem and SymbolFile can't tell the difference between an unsigned char var; and a uint8_t var; because the actual type-node referenced by the variable will always be the underlying raw unsigned char node.

MSVC currently doesn't output lf_alias either, but it would solve some issues for C/C++ and third-party languages. lf_alias appears to be the equivalent of DW_TAG_typedef, so it would result in better feature parity with dwarf debug info.

[Walnut356]

Also involves llvm as this will need to affect debug info generation at compile-time as well

[llvmbot]

@llvm/issue-subscribers-debuginfo

Author: Walnut (Walnut356)

Outlined [here](https://github.com//issues/114906#issuecomment-3152608683).

>Local variables store their type via a type index, this is also true for global variables. Since typedef nodes don't live in the type stream, variables cannot have typedefs as types. <br/><br/>The front-end asks the TypeSystem about the type of a variable, but the TypeSystem and SymbolFile can't tell the difference between an unsigned char var; and a uint8_t var; because the actual type-node referenced by the variable will always be the underlying raw unsigned char node.

MSVC currently doesn't output lf_alias either, but it would solve some issues for C/C++ and third-party languages. lf_alias appears to be the equivalent of DW_TAG_typedef, so it would result in better feature parity with dwarf debug info.

[Walnut356]

I took a look and I think I understand what all needs to be changed for this. I'll give it a try in the next few days here