Allowed placing HTML tags for all input fields in the D&D v2 xblock

See, for example it's hard to tell whether this will actually result in a test for the preservation of HTML - it looks like it, but would require checking multiple files to be sure. Tests is one of these places where too much refactoring can be detrimental, compared to "normal" code.

I would prefer an explicit test - a good way to do this with fixtures is to have a base fixture, which you alter slightly for different explicit tests, like in https://github.com/open-craft/atlas_qualtrics_stats/blob/48e8040bdf9ce51ab5b312171ec60118f5f6d5ad/qualtrics_stats/tests/test.py#L68 for example