Make RenameLocation unique

[DeeSee]

Summary

When a file is indexed by multiple compilation units (e.g. multiple targets in a build system compile or import the same source file), index.occurrences(ofUSR:roles:) returns one entry per unit for the same source position. These duplicate RenameLocations produce overlapping TextEdits in the WorkspaceEdit, which editors reject — VS Code shows "Rename failed to apply edits" with no further detail.

Changes

• Changed locationsByFile to collect rename locations in a Set<RenameLocation> instead of [RenameLocation], effectively making duplicates impossible.
• Made RenameLocation and RenameLocation.Usage conform to Hashable so they can be stored in a Set.
• Sort the set into an array before passing to editsToRename, since the downstream API expects [RenameLocation] and some callers depend on ordering.

Test

• I've added a test case that simulates the issue: it compiles single source file twice with different compilation conditions and then checks that rename doesn't produce duplicate edits. I've verified that this test fails if I rollback the fix.