Ruby 3.1 features

[aibaars]

This pull-request Implements the following items taken from https://rubyreferences.github.io/rubychanges/3.1.html

• Values in Hash literals and keyword arguments can be omitted
• Anonymous block argument
• Expressions and non-local variables allowed in pin operator ^

The following items are not addressed by this pull request as did not yet find a good way to implement them without causing all sorts of grammar conflicts.

• One-line pattern matching (both versions) is no longer experimental
• Inside “endless” method definitions, method calls without parenthesis are allowed

Checklist:

• All tests pass in CI.
• There are sufficient tests for the new fix/feature.
• Grammar rules have not been renamed unless absolutely necessary.
• The conflicts section hasn't grown too much.
• The parser size hasn't grown too much (check the value of STATE_COUNT in src/parser.c).

[aibaars]

@nickrolfe

[tclem]

Grammar changes look reasonable, corpus tests make sense. I spot checked the example tests (ruby_spec) and the results are identical to the last run on main:

Successfully parsed 4259 of 4264 example files (99.9%)

👍