Add translation search highlights

[philmcmahon]

What does this change?

This PR wires in the various bits and pieces needed to show highlights for search results from inside translated text.

As part of this work I've ended up abandoning the dropdown switcher for viewing translations introduced in #780 and instead made the translation views just more tabs in the bottom right. I think the UX here could use some work (as you can get a lot of tabs) but didn't want to put time into dealing with highlights and url query syncing for the translation viewer as part of this bit of work, instead putting it off for some future UX overhaul (hopefully post full typescriptification).

Depends on #783 which should be merged and rebased into this before this is reviewed - it was too awkward working with a js PreviewSwitcher.

The main changes:

• new HighlightableLanguageData which has HighlightableText instead of just string types (the standard LanguageData type is used for to/from elasticsearch, HighlightableLanguageData is constructed based off search results from elastic
• New 'translated body text' chip - we currently don't have an OCR text chip so I just did body text for now. (Pending @hoyla's mega chips overhaul)
• Various helper functions for digging out the heavily nested languageData.text.translation field

How has this change been tested?

• Tested locally
• Tested on playground