[clang-tools-extra] [clangd] Add a unit test suite for HeuristicResolver (PR #121246)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

Updated to take advantage of the new `dependentNameType()` matcher added in https://github.com/llvm/llvm-project/pull/121263.

https://github.com/llvm/llvm-project/pull/121246