Note that we cannot write tests for these at the moment. Passing
```
-enable-experimental-feature DefaultIsolationPerFile
```
to the extractor results in:
```
error: experimental feature 'DefaultIsolationPerFile' cannot be enabled in production compile
```
Note that it does not seem to be possible to write test that exercise this
code. Passing `-enable-experimental-feature KeyPathWithMethodMembers` to the
extractor results in:
```
error: experimental feature 'KeyPathWithMethodMembers' cannot be enabled in production compiler
```
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.
This improves the implementation of the generated parent/child
relationship by adding a new `all_children` field to `ql.Class` which
lists all children (both direct and inherited) of a class, carefully
avoiding duplicating children in case of diamond inheritance. This:
* simplifies the generated code,
* avoid children ambiguities in case of diamond inheritance.
This only comes with some changes in the order of children in the
generated tests (we were previously sorting bases alphabetically there).
For the rest this should be a non-functional change.
These are currently added implicitly by the compiler in the context of
`if`/`switch` expressions. In the future, there might be explicit
`then <expr>` statement useful for cases where one would like to add
more than one statement in the branch, to mark what value to actually
use.
See https://forums.swift.org/t/pitch-multi-statement-if-switch-do-expressions/68443
