Only set parents for parse trees in the LS for the syntactic trees.

we don't need this for the semantic trees because the compiler will set them all during
the binding.
Merge pull request #1432 from Microsoft/isOpenVersion2

Only set parents for parse trees in the LS for the syntactic trees.
Merge branch 'master' into sourceFileUpdate

Conflicts:
	src/services/services.ts
	tests/cases/unittests/incrementalParser.ts