Fix fatal in frame:callParserFunction

If the parser function returns 'isChildObj', we need to create a child
frame to expand the wikitext returned by the parser function. And when
we pass the arguments to the new frame, we need to pass them through the
preprocessor's newPartNodeArray() first.

Bug: 50863
Change-Id: Ieb7cc7007288de1f7d2cd2458f068affe695e8af