Fixes#106445 by using the lexer to find the correct range for the
removal FixIts. Previously the ranges that were generated assuming no
unsurprising formatting, which for the most part works. Being correct in
all cases requires using the lexer to find the bounding tokens for the
region to remove.
As part of this it adds Sema::getRangeForNextToken to wrap
Lexer::findNextToken.
