[lldb][DWARFASTParserClang] Correctly resolve imported namespaces during expression...

[lldb][DWARFASTParserClang] Correctly resolve imported namespaces during expression evaluation

**Summary**

This patch makes the expression evaluator understand
namespace aliases.

This will become important once `std::ranges` become
more widespread since `std::views` is defined as:

```
namespace std {
namespace ranges::views {}

namespace views = ranges::views;
}
```

**Testing**

* Added API test

Differential Revision: https://reviews.llvm.org/D143398