[lldb][Format] Unwrap references to C-strings when printing C-string summaries (#174398)

Depends on:
* https://github.com/llvm/llvm-project/pull/174385

(only last commit is relevant for this review)

The `${var%s}` format isn't capable of formatting references to
C-strings. So the summary for those becomes `<no value available>`. This
patch prevents the system C-string formatter from applying to
references, which means the summary for such types will be empty. This
prompts LLDB to instead print the child, which is the referenced
C-string.

Before:
```
(lldb) v ref
(const char *&) ref = 0x000000016fdfe960 <no value available>
```

After:
```
(lldb) v ref
(const char *&) ref = 0x000000016fdfec40 (&ref = "hi")
```

An alternative would be to support references in the `ValueObject` dump
methods. We assume C-string are pointers/arrays in a lot of places, so
such a fix would be a more intrusive undertaking, and I'm not sure we
would want to support references there in the first place. So for now I
went with the fallback logic in this PR.