[clang] [clang][AST] Add 'IgnoreTemplateParmDepth' to structural equivalence cache (PR #115518)

[Balázs Kéri via cfe-commits]

balazske wrote:

I had another simple fix when the cache is used only if `IgnoreTemplateParmDepth` is false which is the often used case. During one structural equivalence comparison `IgnoreTemplateParmDepth` does not change, just one set of the cached values (for `IgnoreTemplateParmDepth`) is used.

https://github.com/llvm/llvm-project/pull/115518