This collapses all generated test QL sources into a single one per
directory, using query predicates to run the different tests.
This should improve the time required to run generated tests.
* `variables` under `CaseStmt` are now AST children, which solves
orphan `VarDecl`s in that case
* reordered `CaseStmt` AST children to be `labels > variables > body`
(was `body > labels`)
* made `NamedPattern::getVarDecl` an extracted property instead of
`getName`
* The above led to duplicate DB entities because of a quirk in the
Swift compiler code. This is solved by tweaking the extraction of
`variables` under `CaseStmt` to not use `getCaseBodyVariables`.
