[clang] [clang-tools-extra] [clang][CodeComplete] Use HeuristicResolver to resolve pointee types (PR #121315)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

> This made me realize that `HeuristicResolver::getPointeeType()` actually has a deficiency where it incorrectly discards the cv-qualifiers of the returned pointee type. I'll fix that in a dependent patch before proceeding with this.

Filed https://github.com/llvm/llvm-project/issues/123549 to track this.

https://github.com/llvm/llvm-project/pull/121315