[clang-format] Use wider comment prefix space rule

This commit changes the condition of requiring comment to start with
alphanumeric characters to make no change only for a certain set of
characters, currently horizontal whitespace and punctuation characters,
to support wider set of leading characters unrelated to documentation
generation directives.

Reviewed By: HazardyKnusperkeks
Differential Revision: https://reviews.llvm.org/D118869