Add embedded font family test.

[skynavga]

See w3c/ttml2#1049 (comment).

[nigelmegitt]

The added test checks only for validation of invalid font family names. Still to do:

• validation of valid font family names that differ from generic names only by change of case;
• presentation of text whose tts:fontFamily computed value is a generic family name and a font is defined with the same generic family name in the family attribute - the output must use the default font not the included/referenced font.

[skynavga]

While we can add as many tests as we like, you asked for a test, and the merged PR adds such a test. There is no requirement that says what must be tested or defines completeness with regard to testing. I'm certain that for every test that exists in the TS, you can think of N more tests to add (no matter how large you want to make N). If you want to add more tests, then open new issues along with PRs that satisfy them. In the mean time, I am re-closing this issue.

[nigelmegitt]

I don't agree with @skynavga 's summary from 26 March 2019. This is the generic ticket to add font family tests associated with the normative specification changes in TTML2 from w3c/ttml2#1049. That change introduced 3 individually testable things, and it's my position that we should test all of them:

1. generic font family names in font elements are considered an error.
2. comparison of font family names with generic font family names is case sensitive.
3. referenced font resources where the font family name matches a generic font family name must be ignored for presentation.

We have tested only the first one therefore we have not completed this issue.

[skynavga]

Moving follow-on work from #201 (comment) to #254 and re-closing this issue.