Most `SemaAnnotator`s don’t actually care about the char source range. Instead, they only care about the start location of the reference, which is also included in `SourceRange`. Computing a `CharSourceRange` from a `SourceRange` is kind of expensive because it needs to start a new lexer.
To avoid this overhead, pass `SourceRange` to `SemaAnnotator::passReference` and related functions and let the clients compute the `CharSourceRange` when needed.
This reduces the overhead of index-while-building by about 10%.
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