Turn an uncorrelated EXISTS / NOT EXISTS subquery into an INNER join with one row, since that gives completely flexible ordering that SEMI / ANTI join does not.
Add some tests.
Calculate tables here since already walking the tree. Fixes unit tests that didn't run some rules.
merge MMcM: Handle uncorrelated semi join better

Merge pull request #1219 from MMcM/sql-layer/uncorrelated-semi-join
https://github.com/FoundationDB/sql-layer/pull/1219