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%.
Although I don't plan to bring over new assertions wholesale
into the current qualification branch, it's entirely possible
that various minor changes in main will use the new assertions;
having this basic support in the release branch will simplify that.
(This is why I'm adding the includes as a separate pass from
rewriting the individual assertions)
It's not clear that its worth keeping this as a
base class for SerializedAbstractClosure and
SerializedTopLevelCodeDecl, most clients are
interested in the concrete kinds, not only whether
the context is serialized.
