Implement 'textBaseline' SDF property

[frank-weindel]

This was originally intended for #107 but ran out of time to address it for now with other higher priority work. We should be able to easily support 'alphabetic', 'top', 'middle', and 'bottom', however the other specialized baselines might prove challenging as we do not have that baseline data in the generated SDF font data.

[github-actions]

This issue is stale because it has been open for 180 days with no activity. It will be closed in 7 days if no further activity occurs.