We need the output content language when fetching HTML in VE
so this needs to match whatever parsoid gives us. In order for
this to happen, we need to loop in more data to the parser output
after parsing. This patch adds that more relevant data and
exposes it via a public method: `getHtmlOutputContentLanguage()`
In addition, this patch fixes a bug that was introduced in the
PageBundleParserOutputConverterTest when setting extension data
on parser output (L#64).
Follow-up: I33076c359ee45719c1c4ef63f77c1f1285951d0c (test fix)
Change-Id: I06bf9f575ed5a2521cf4b2c42fc6e0e7faab6bc0
9397a235c9