Deprecate edge-case get and normalizeTuple behavior ahead of #3852

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.