[lang-test] Use tree dumps for regression tests

[oowekyala]

This makes it possible to write parser tests that just compare a dump of the AST against a baseline. This can make for cheap regression tests, which can be useful

• in language modules which use an external parser, and so the structure can easily change when upgrading the parser library (eg Javascript, Apex, Scala).
• in newer language modules, where the amount of tests to write to get decent parser coverage is overwhelming (eg Scala)
• to support parser features that may easily change in the future, eg Java preview features

I extracted the AST printer from the designer codebase, so that the designer can use this printer in the next update

This adds a few tests for Scala as a PoC

[pmd-test]

	1 Message
📖	This changeset introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 0 errors and 0 configuration errors. Full report
✅	This changeset introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 0 errors and 0 configuration errors. Full report

Generated by 🚫 Danger

[adangel]

Thanks