IsPattern coercions aren't properly implemented since they rely on
doing a runtime cast, which can fail for things like function subtyping.
Make clients choose what behavior they want. Unfortunately we need to
preserve the current behavior in places since it's relied upon for
things like exhaustivity checking. We ought to properly implement
coercion handling, then we should be able to remove this.
Lexer should always set `Token.CommentLength` correctly because it
necessary for restoring to the token position with comments.
Otherwise, 'Token::isAtStartOfLine()' might not correctly set.
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)
LLVM is presumably moving towards `std::string_view` -
`StringRef::startswith` is deprecated on tip. `SmallString::startswith`
was just renamed there (maybe with some small deprecation inbetween, but
if so, we've missed it).
The `SmallString::startswith` references were moved to
`.str().starts_with()`, rather than adding the `starts_with` on
`stable/20230725` as we only had a few of them. Open to switching that
over if anyone feels strongly though.
