Add eval construct / wire up to Simala's #eval decl; fix / defer some Langium grammar issues; fix some backend parser bugs

[ym-han]

1. Closes Wire it up to Well-Typed's evaluator for concrete evaluation #19 , Make basic version of wrapper CLI(s) #71 , [Parser] Fix InfixPredicateApp vs InfixActionApp bug / design issue (or just disable ActionApp for now) #76 . Surface syntax for #eval is @REPORT; happy to change this if people have other ideas.
2. Also enables function application for nullary functions -- grammar had previously unintentionally prevented that
3. Fixes [ToSimala] Look into issue / bug with translation #80
4. Fixes unary op backend parser bug

Note

• There is a naming / scoping thing I'll need to check / think through ([ToSimala] Scoping: Check if the way I'm translating names is correct --- might need to just use Uniques instead of Uniques concatenated with reftext #79 ); this shouldn't be hard
• Need to add tests; haven't tested very much yet

[fendor]

LGTM!

[ym-han]

LGTM!

Thank you for looking through this!