This is a follow-up for https://gerrit.wikimedia.org/r/178582

We now strip meta/link tags during parser tests normalization. We need to explicitly add tests for the <meta>/<link> tags defined in the Parsoid DOM spec. These include Meta/link tags for *include*, magic words, behavior switches. (Check this against the blacklist changes in https://gerrit.wikimedia.org/r/178582 to ensure we've got everything.)

Four ways to do this. They all start by writing new test cases with the targetted flags.

Then:

1. Enable only html2wt testing on these new tests. The <meta> and <link> tags aren't stripped out of tests case input. (easy)

2. Add a special "preserve meta" parser tests option, and use this flag for these tests.

3. Add a special "strip meta" parser tests flag, and use it on all the *other* tests whenever parser tests would otherwise spuriously fail due to <nowiki> insertion, etc. (harder)

4. Strip <meta> in *non* parsoidOnly normalization, and *preserve* meta for parsoid-only tests. This is probably what we should have done in the first place. There's probably a good reason we did it backwards, which we'll discover once we try it.