Additional FXL Layout tests

[iherman]

Three new tests:

• Viewport w/h are set to device-width and device-height, respectively
• No viewport is set (should use device-width and device-height)
• Erronuous viewport is set (should use device-width and device-height)

Edited on 2022-10-15: as a result of #235 (comment) the content of the PR has changed:

• Viewport w/h are set to device-width and device-height, respectively
• Reading systems SHOULD attempt to extract 'width' and 'height' values even if the tag's syntax is invalid.
• Reading system should use the first declaration of a 'width' or 'height' (i.e., ignore repeated declarations).

Also, an older test has been updated to use patterns instead of colors only, to make it usable for b/w/ displays.

[davemanhall]

Looks good - able to open all tests.

[iherman]

These tests may have to be changed/adapted to the outcome of w3c/epub-specs#2453. Should be considered as a draft for the time being.

[rdeltour]

As suggested in a comment inline: the test case for invalid viewport meta only tests one possible (invalid) pattern. More cases can be conceived, but I don't know if the intent is to be thorough or to have only one key test.