Problem
-------
Currently we use `$.expression` everywhere even though it often
requires much narrower set of expressions.
Solution
--------
Now that we've gained some memory budget, this adds
`_simple_expression`, mirroring the EBNF, and adjusts
`infix_expression` etc to use narrower choice of expression tokens.
With this change, the smoke test for Scala 2 library jumps to 95%.
Problem
-------
My grep has a bug, so *.sh file changes are detected as C change.
Solution
--------
1. Add backslash before dot.
2. Bump up the expected Dotty score.
This adds real-world integration test using scala/scala and Dotty
compiler code base.
The expected parse success% is currently hardcoded, but at least
we'll catch if this number degrades.