[clang][NFC] Remove CXXRecordDecl::lookupDependentName() and its helpers (#128392)
This function has been superseded by
HeuristicResolver::lookupDependentName(), which implements the same
heuristics and more.
Porting note for any out-of-tree callers:
```
RD->lookupDependentName(Name, Filter);
```
can be replaced with:
```
HeuristicResolver(RD->getASTContext())->lookupDependentName(Name, Filter);
```