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/tcommandindent.nim

@@ -0,0 +1,16 @@
+when false: # parse the following
+  let foo = Obj(
+    field1: proc (src: pointer, srcLen: Natural)
+                    {.nimcall, gcsafe, raises: [IOError, Defect].} =
+      var file = FileOutputStream(s).file
+
+      implementWrites s.buffers, src, srcLen, "FILE",
+                      writeStartAddr, writeLen,
+        file.writeBuffer(writeStartAddr, writeLen)
+    ,
+    field2: proc {.nimcall, gcsafe, raises: [IOError, Defect].} =
+      flushFile FileOutputStream(s).file
+    ,
+    field3: proc () {.nimcall, gcsafe, raises: [IOError, Defect].} =
+      close FileOutputStream(s).file
+  )