[FileCheck, test] Rename checkWildcardRegexCharMatchFailure

Proposed edit https://reviews.llvm.org/D97845#inline-922769 in D97845
suggests the checkWildcardRegexCharMatchFailure function name is
misleading because it is not clear it checks for a match failure on each
character in the string parameter. This commit renames it to an
hopefully clearer name.

Reviewed By: jdenny

Differential Revision: https://reviews.llvm.org/D98343