This PR implements completion for the simple cases of async and void in
a local function context. What it misses cases where parsing incorrectly
considers bare modifiers to be local variable declaration statements
rather than local function declaration statements. This is tracked by
bug #14525.

Fixes #8616
Fixes #8617

Rename intenral code to 'FindUsages' so it better reflects that it can present results for more than just FindReferences.

Use an EquivalenceKey for 'InlineDeclaration' so we don't get multiple offerings of the same fix on a single line.

Pull common FixAll logic into some helper base types that we can use across many of our code style fixes.