no ropes WIP (#20433)

* refactorings in preparation for ropes elimination of the C code generator; mostly the usual ': Rope' -> 'result: var Rope' rewrite
* rewrote ccgcalls.nim
* refactored ccgexprs.nim
* ccgliterals: refactoring
* refactoring: code dealing with name mangling
* refactoring: getRecordFieldsAux
* ropes are strings (insert obscene joke here)
* optimize JS code gen
* optimizations and code improvements
* more optimizations
* final cleanups

compiler/semtypes.nim

@@ -824,7 +824,7 @@ proc semRecordNodeAux(c: PContext, n: PNode, check: var IntSet, pos: var int,
       f.options = c.config.options
       if fieldOwner != nil and
          {sfImportc, sfExportc} * fieldOwner.flags != {} and
-         not hasCaseFields and f.loc.r == nil:
+         not hasCaseFields and f.loc.r == "":
         f.loc.r = rope(f.name.s)
         f.flags.incl {sfImportc, sfExportc} * fieldOwner.flags
       inc(pos)