Change percentage values to be stored as numbers.

We were storing percentage values as strings with [num]%. The spec
says to store these as numbers instead. In the case of line, which
can be an integer or a percentage, we have to differentiate between
the two with the snap-to-lines flag. We have to expose this in the
WebIDL as well so we have to do the conversion at some point. I think
it's best to just store it as a number right off the bat.
Remove cue-settings-position.vtt.

This should have been removed when the test was switched over to
work with the new test.list files.
Move cue setting size tests over to new test.list files.
Move bold span tests to new test.list files.