feat: add support for dynamic class constant fetch

[calebdw]

Checklist

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

Hello!

This adds support for dynamic class constant fetch---subsequently closes #197 after #205 is merged. (note this is branched from #192).

I went ahead and kept the same class_constant_access_expression node...I'm not sure if we need a separate dynamic node.

Thanks!

[calebdw]

See #214