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/sigmatch.nim

@@ -2505,6 +2505,11 @@ proc instTypeBoundOp*(c: PContext; dc: PSym; t: PType; info: TLineInfo;
     if f.kind in {tyRef, tyPtr}: f = f.lastSon
   else:
     if f.kind == tyVar: f = f.lastSon
+  #if c.config.selectedGC == gcDestructors and f.kind == tySequence:
+  # use the canonical type to access the =sink and =destroy etc.
+  #  f = c.graph.sysTypes[tySequence]
+  #echo "YUP_---------Formal ", typeToString(f, preferDesc), " real ", typeToString(t, preferDesc), " ", f.id, " ", t.id
+
   if typeRel(m, f, t) == isNone:
     localError(c.config, info, "cannot instantiate: '" & dc.name.s & "'")
   else: