Remove redundant zero-initialization of struct temps with GC fields. (dotnet/coreclr...

Remove redundant  zero-initialization of struct temps with GC fields. (dotnet/coreclr#13868)

Remove redundant  zero-initialization of struct temps with GC fields.

Structs with GC pointer fields are fully zero-initialized in the prolog if compInitMem is true.
Therefore, we don't need to insert zero-initialization for the result of newobj or for inlinee locals
when they are structs with GC pointer fields and the basic bock is not in a loop.

Commit migrated from https://github.com/dotnet/coreclr/commit/c77ad480298300b655ced317bf25b1fe4f27ceb3