ref/call spans should cover identifiers only

[zrlk]

Historically, the source anchor for ref/call covered the entire calling expression. Users generally disliked the resulting decorations and they were suppressed, as the ref to the callee was sufficient. To simplify the schema and make certain postprocessing tasks easier, the source anchor for a ref/call should be the same as the source anchor for that corresponding ref.

Syntactic forms that do not have an equivalent corresponding ref (e.g., implicit coercions) should maintain their existing behavior.

We do not currently propose dropping the ref as user code may rely on it, but expect to do so in the future.