Issue:
#I8GI02:[ArkTS] Support undefined type

Reason (target, resolving problems, etc):
Support nullish types and 'undefined' value

Description:
Support nullish types and 'undefined' value

Test scenarios (new, modified, affected functions):
Parser,checker,codegen
All required pre-merge tests passed. Results are available in the ggwatcher.

Change-Id: I1c1153803359bb5cc7defcd427b0addb581c5cab