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

[Balázs Kéri via cfe-commits]

balazske wrote:

It is a realistic requirement that new similar parameters are added, I had already an (experimental) fix where this is needed. Still I like better the solution with separate caches because efficiency reasons (`IgnoreTemplateParmDepth = true` is rarely used, not at all for C code). For new parameters we have the similar set of choices (add more new caches or extend cache key or not use the cache at all).

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