Named arguments in commands + many grammar fixes (#20994)

* Breaking parser changes, implement https://github.com/nim-lang/RFCs/issues/442

Types are separated from expressions and better reflected in the grammar.

* add test

* more accurate grammar

* fix keyword typedescs

* accept expressions in proc argument lists

* CI "fixes"

* fixes

* allow full ref expressions again, adapt old tests

* cleanup, fix some tests

* improve grammar, try and revert semtypes change

* restrict sigil binding to identOrLiteral

* fix, should have caught this immediately

* add changelog entry, fix double not nil bug

* correct grammar

* change section

* fix

* real fix hopefully

* fix test

* support LL(1) for tuples

* make grammar.txt too

tests/parser/tcommand_as_expr.nim

@@ -36,3 +36,12 @@ echo f -4
 
 echo int -1 # doesn't compile
 echo int `-` 1 # compiles
+
+var num = 1
+num += int 2
+doAssert num == 3
+
+import options
+var opt = some some none int
+opt = some some none int
+opt = some none Option[int]