gc: destructors is beginning to work (#10483)

* kochdocs.nim: code cleanup
* docgen: nicer indentation
* parser.nim: code cleanup
* fixes #10458
* make tests green again
* make =destroy mixins
* gc:destructors: produced C code is almost working
* --gc:destructors simple program compiles (but leaks memory)
* gc:destructors make examples compile in C++ mode
* destructors: string implementation bugfixes
* strs.nim: minor code cleanup
* destructors: builtin seqs are beginning to work
* remove debugging helpers

compiler/semasgn.nim

@@ -316,6 +316,11 @@ proc liftBody(g: ModuleGraph; typ: PType; kind: TTypeAttachedOp;
               info: TLineInfo): PSym =
   if typ.kind == tyDistinct:
     return liftBodyDistinctType(g, typ, kind, info)
+  when false:
+    var typ = typ
+    if c.config.selectedGC == gcDestructors and typ.kind == tySequence:
+      # use the canonical type to access the =sink and =destroy etc.
+      typ = c.graph.sysTypes[tySequence]
 
   var a: TLiftCtx
   a.info = info