Deprecate edge-case get and normalizeTuple behavior before fixes

Requires #4123.

PR #3852 changes some edge case behavior for get and normalizeTuple. Ahead of those changes, this commit introduces deprecation notices.

  * Deprecate get for local paths on global contexts, only if they
    return data.
  * Deprecate normalizeTuple calls that return a non-global contenxt
    and a simple global path.

/cc @ebryn @wagenet
It was a public interface. Unsure if it is public post ES6