Rollup merge of #143914 - shepmaster:mismatched-lifetime-syntaxes-rewording, r=traviscross,jieyouxu

Reword mismatched-lifetime-syntaxes text based on feedback

Key changes include:

- Removal of the word "syntax" from the lint message. More accurately, it could have been something like "syntax group" or "syntax category", but avoiding it completely is easier.
- The primary lint message now reflects exactly which mismatch is occurring, instead of trying to be general. A new `help` line is general across the mismatch kinds.
- Suggestions have been reduced to be more minimal, no longer also changing non-idiomatic but unrelated aspects.
- Suggestion text no longer mentions changes when those changes don't occur in that specific suggestion.

r? ``@jieyouxu``

Author: matthiaskrgr