Add control of ParagraphSpacingPolicy to remove additional line breaks

[charrondev]

In my usage I find I prefer to control spacing between lines using ParagraphSpacing instead of having additional breaks inserted.

In this PR, I am adding a new policy enum to control this. The defaults remain the same as previously.

The updated README should give a good indication of how to use this, but the crux of it is, the additional breaks are removed when this is set.

API Decisions

I ended up making this a policy because I figure if someone wants this they likely want it to be consistent through the whole document, rather than having it be controlled be tag declarations or styles.

Tests

I was having a bit of trouble getting the tests setup to actually write any for this. I guess it might make sense to add some snapshot tests, but I would need to know what simulator size you were using for them (and any other recommendations you might have). When I just downloaded and ran the test plan it had a bunch of subtle diffs in the snapshots.

[zhgchgli0718]

thanks for contributing, I'll fix CI/CD Tests Flow and merge PR ASAP.