Add context to SDE extension

[rob-reynolds]

As a processor of SDE extensions I need to be able to tie the SDE extension back to the SDE definition in the Measure.

The contained SDE entries include an extension that addresses this, but by tying it back to the CQL Expression. Ideally both contained SDEs and Resource SDEs would link back to the Measure.

This effort requires design. Implementation is blocked for said design.