The initial implementation assumed that the consuming editors would
de-duplicate rename locations. In fact, vscode treats overlapping rename
locations as distinct and errors when trying to preview the renames.
This commit updates the language service to de-duplicate exact file+span
matches before returning rename and reference locations.
While vscode _does_ de-duplicate reference results, it still makes sense
to de-duplicate them on our side when possible to make tests more
understandable. If a template has 3 instances of a variable, it makes
sense to get get 3 reference results rather than 4+ with some duplicates.
PR Close#40454
402e2e6189