We weren't renaming all occurrences of 'x' in the cases like the below:
case .first(let x), .second(let x):
print("foo \(x)")
fallthrough
case .third(let x):
print("bar \(x)")
We would previously only rename occurrences within the case statement the query
was made in (ignoring fallthroughs) and for cases with multiple patterns (as in
the first case above) we would only rename the occurrence in the first pattern.
Set local discriminator for all local `VarDecl`s. Otherwise, they cannot
be discriminated with USRs. This change is needed for rename refactoring which
uses USR for discrimiating variable names.
https://bugs.swift.org/browse/SR-7205,
rdar://problem/34701880
