[clang-tidy] Deal with keyword tokens in preprocessor conditions

When a "keyword" token like __restrict was present in a macro condition,
modernize-macro-to-enum would assert in non-release builds.  However,
even for a "keyword" token, calling getIdentifierInfo()->getName() would
retrieve the text of the token, which is what we want.  Our intention is
to scan names that appear in conditional expressions in potential enum
clusters and invalidate those clusters if they contain the name.

Also, guard against "raw identifiers" appearing as potential enums.
This shouldn't happen, but it doesn't hurt to generalize the code.

Differential Revision: https://reviews.llvm.org/D123349

Fixes #54775