Support for italic bold / nested tags

[vvidday]

Currently, working with text that is both bold and italic causes a few functions to break

• Arrow key navigation doesn't work if italic bold text is at front/back of block
• Merge doesn't work if italic bold text is at the front of the block that is being merged
• Split doesn't work if initiated from within the italic bold text
• Conversion via search doesn't delete search term if initiated from within italic bold text

Issues are mainly due to the tags being nested, since most functions currently only work for one layer of nested tags

Video

Fix would require a decent amount of refactoring to support nested tags