Factors the cursor_info requests into a single API to asynchronously
make the sourcekitd cursor_info request and wrap the result for easier
consumption from Swift (but not other processing).
Also, cleanup the now unused extensions on Hover that were superceded by
symbolInfo.
Rework LineTable. Now that line table is just a collection of `Substring`.
Derive UTF16/UTF8 offset from corresponding view of the content String.
Added several methods to translate between line/UTF(8|16)column and
UTF8 offset.
Resolves: https://bugs.swift.org/browse/SR-9311
We have multiple copies of llvm symbols (indexstoredb, indexstore,
llbuild via swiftpm, and sourcekitd), so it's important to keep them
isolated. In practice this seems to have started breaking after we
updated swiftpm and llbuild was added, but it was already a potential
issue before that. The most egregious issue is if you build sourcekit
with assertions, it enables ABI-breaking checks in llvm. On macOS this
dlopen behaviour is already the default.
