An optimizer for ARC (#14962)

* WIP: an optimizer for ARC
* do not optimize away destructors in 'finally' if unstructured control flow is involved
* optimized the optimizer
* minor code cleanup
* first steps to .cursor inference
* cursor inference: big steps to a working solution
* baby steps
* better .cursor inference
* new feature: expandArc for easy inspection of the AST after ARC transformations
* added topt_cursor test
* adapt tests
* cleanups, make tests green
* optimize common traversal patterns
* moved test case
* fixes .cursor inference so that npeg compiles once again
* cursor inference: more bugfixes

Co-authored-by: Clyybber <darkmine956@gmail.com>

compiler/commands.nim

@@ -866,6 +866,9 @@ proc processSwitch*(switch, arg: string, pass: TCmdLinePass, info: TLineInfo;
   of "expandmacro":
     expectArg(conf, switch, arg, pass, info)
     conf.macrosToExpand[arg] = "T"
+  of "expandarc":
+    expectArg(conf, switch, arg, pass, info)
+    conf.arcToExpand[arg] = "T"
   of "oldgensym":
     processOnOffSwitchG(conf, {optNimV019}, arg, pass, info)
   of "useversion":