Fix bug where inline nodes didn't trigger wrapping

When encountering an inline node (i.e. content node that's not a text
node) within a branch node that's not a content branch node, the
converter should start a wrapper. But it doesn't do this, it only opens
wrappers for text nodes and annotations.

Fixed this in the converter, added a test for it, and fixed an existing
test that asserted the broken behavior.

Change-Id: I6e143e21e68b68f0d85b8772e24a2d3a5d465410
Merge "Fix bug where inline nodes didn't trigger wrapping"