Fix match return vertex undefined labels (#553)

* add support for tags()

* add flattenTags() to retrieve empty tags

* add basic test

* refactor

* refactor match planner

* modify iterator

* add test cases with tags()

* format changes

* refactor code with getAllLatestTagSchema()

* address comments

* modify tck frame and add tests for int vid

* replace getAllVerTagSchema() with getAllLatestVerTagSchema() in graph

* address comments

Co-authored-by: Yee <2520865+yixinglu@users.noreply.github.com>
Co-authored-by: Shylock Hg <33566796+Shylock-Hg@users.noreply.github.com>