Columns block: difficult to exit

[annezazu]

Similar to #52773 and originally noted here #50129, the columns block is difficult to exit with enter:

hard.to.exit.a.columns.block.mov

The only way to exit is through insert before/after or to select the parent and find the in between inserter. This feels overly painful!

[Mamaduka]

The Group and Quote block support exists on Enter at the last block (it should be an empty paragraph). This is enabled via the __experimentalOnEnter supports flag. See #39911.

Currently, the method doesn't support nested blocks like Columns. When they're supported, we can enable it here.

Cc @oandregal.

[oandregal]

cc @ellatrix as she has the most context about the current state of that work.