This PR is a subset of the commits made in
https://github.com/swiftlang/llvm-project/pull/10710.
The most notable change is the addition of `PrefixRange` and
`SuffixRange` which are a catch-all to track anything after or before a
function's demangled name. In the case of Swift, this allows to add
support for name highlighting without having to track the range of the
scope and specifiers of a function (this will come in another PR).
