[lldb][Format] Make function name frame-format variables work without debug-info (#137408)
This patch makes the frame-format variables introduced in
https://github.com/llvm/llvm-project/pull/131836 also work when no
debug-info is available. Previously, we assumed `sc.function` was
available, but without debug-info we might only have `sc.symbol`. We
don't really need the `sc.function` apart from when formatting
arguments.
For the function arguments case I added a fallback that will just print
the arguments we get from the demangler (which is what LLDB does for
stacktraces with no debug-info anyway). Ideally we'd have a separate
`FormatEntity::Entry::Type::FunctionArguments` that will just print the
arguments from the demangler and have something like the following in
the `plugin.cplusplus.display.function-name-format`:
```
{ ${function.formatted-arguments} || ${function.arguments} }
```
I.e., when we can't format the arguments, print the ones from the
demangler. But we currently don't have the `||` operator in the
frame-format language yet.