Put YAML IT source into a separate module

This will make the test-jar that FTS uses more self-contained (just test sources, no Java classes) and lay the groundwork for eventually switching which driver(s) is used.

I think that it's set up so that no one's YAML test workflow should be significantly impacted. If you run from Maven at top-level, the reactor will give it files in the sibling module. Everything should still be clickable in the IDE. If you run Maven inside fdb-sql-layer-core, the sibling test-jar will be used, but the tests will still run and errors should include comprehensible relative pathnames.

A small change is the prefix for the various system properties that control selecting individual YAML tests. It is now just the package name, not the specific runner class.

Jenkins and FTS will have to react, but shouldn't fail on merge of this branch itself.