stop recursive validity checks for nodes

[OmarTawfik]

We query for node completeness/correctness recursively during parsing, for both valid and invalid inputs. For example Match::is_full_recursive(), which will happen for any ChoiceHelper even at root of the tree (like SourceUnitMember). There could be other places as well that create a Cursor during parsing do check for sub-trees recursively.

We should revisit this once #808 is complete.

One solution is to track this information via a field on the ParserResult instead, and propagate that field upwards instead.