nitcc add groups and small improvments

[privat]

Add groups in the parser, that are anonymous productions enclosed by parenthesis.

foo = x (bar baz) y | z ;

is equivalent with

foo = x anon0 y | z ;
anon0 = bar baz ;

This becomes handy when combined with the modifies +, ? and *.

foo = x (bar baz)+ y | z ;

is equivalent with

foo = x anon0+ y | z ;
anon0 = bar baz ;

that is equivalent with

foo = x anon1 y | z ;
anon1 = anon1 anon0 | anon0 ;
anon0 = bar baz ;

Note: This PR is a fork of #2836

[github-actions]

Test Results

    67 files     314 suites   15m 59s ⏱️
14 174 tests 13 633 ✅ 541 💤 0 ❌
14 230 runs  13 674 ✅ 556 💤 0 ❌

Results for commit a82ff72.

♻️ This comment has been updated with latest results.