These don't make sense for PDB on Windows

This were failing on Windows CI with errors like:
```
22: (lldb) bt
23: * thread #1, stop reason = breakpoint 1.1
24:  frame #0: 0x00007ff7c5e41000 TestFrameFormatFunctionFormattedArgumentsObjC.test.tmp.objc.out`func at main.m:2
25:  frame #1: 0x00007ff7c5e4101c TestFrameFormatFunctionFormattedArgumentsObjC.test.tmp.objc.out`bar + 12 at main.m:3
26:  frame #2: 0x00007ff7c5e4103c TestFrameFormatFunctionFormattedArgumentsObjC.test.tmp.objc.out`main + 16 at main.m:5
27:  custom-frame '()'
     !~~~~~~~~~~~       error: no match expected
28:  custom-frame '(__formal=<unavailable>)'
```

Adds new frame-format variables and implements them in the CPlusPlusLanguage plugin.

We use the `DemangledNameInfo` type to retrieve the necessary part of the demangled name.

https://github.com/llvm/llvm-project/pull/131836