Reverse Index Transform implementation

[ctsims]

Summary

Implements the necessary index table interface methods for
dimagi/commcare-core#1283

and a test for the optimization trigger.

Note - Needs to be rolled in with the formplayer merge, will fail until then.

Feature Flag

N/A

Product Description

N/A

Safety Assurance

• If the PR is high risk, "High Risk" label is set
• I have confidence that this PR will not introduce a regression for the reasons below
• Do we need to enhance manual QA test coverage ? If yes, "QA Note" label is set correctly

Automated test coverage

Unit tests cover the new test structure.

Safety story

Other optimization tests currently have poor coverage of their actual effect on test query plans. The tests cover regressions in query output (IE: whether an engine change results in the expressions providing a different response) but do not really currently cover comprehensively that expected optimizations process. I think we should implement those checks on more of the regressions before incorporating the change.