borrow checking (#15282)

* refactoring: move procs to typeallowed.nim
* frontend preparations for first class openArray support
* prepare the code generator for first class openArray
* code generation for first class openArray; WIP
* code generation for open arrays, progress
* added isViewType proc
* preparations for borrow checking
* added borrow checking to the front end

compiler/options.nim

@@ -162,7 +162,8 @@ type
       ## which itself requires `nimble install libffi`, see #10150
       ## Note: this feature can't be localized with {.push.}
     vmopsDanger,
-    strictFuncs
+    strictFuncs,
+    views
 
   LegacyFeature* = enum
     allowSemcheckedAstModification,