Submission/dzenana.t web idl

Submit WebIDL tests for HTML "sections" and "grouping-content".

The WebIDL tests mean to cover the HTML "sections" and "grouping-content" sections.  However, you'll see that there's not just 1 but 5 flavors of each test file, as I'm not sure which approach is the most desired:  

- the "dummies" approach which I saw in existing tests (the "untested" IDL is a bare skeleton)  (-->  ~50 tests / file)

- the "full IDL" approach, in which the "untested" IDL contains all the background WebIDL to support the "tested" IDL  (-->  ~1500 tests / file)

- the "all tested" approach, in which *all* the IDL is tested along with the object(s), because, as was recently written on the list, chugging through many / redundant tests is cheap, so "why not".  (-->  ~2000 tests / file)

- the "prevent multiple" approach, by which many interfaces can be just tested once within each file.  This may be contrary to the "why not" approach, but the API exists, so here it is being used (although separate test files still duplicate tests)  (--> ~250 tests / file)

- the "prevent multiple but test all IDL" approach, which is perhaps an odd compromise but aims to maximize the number of unique tests performed.  (-->  ~850 tests / file)

I'll be curious to see which one you cherry pick to include in the test suite (if any).  

Thank you in advance for any feedback!