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>

doc/advopt.txt

@@ -122,6 +122,8 @@ Advanced options:
                             use the provided namespace for the generated C++ code,
                             if no namespace is provided "Nim" will be used
   --expandMacro:MACRO       dump every generated AST from MACRO
+  --expandArc:PROCNAME      show how PROCNAME looks like after diverse optimizations
+                            before the final backend phase (mostly ARC/ORC specific)
   --excludePath:PATH        exclude a path from the list of search paths
   --dynlibOverride:SYMBOL   marks SYMBOL so that dynlib:SYMBOL
                             has no effect and can be statically linked instead;