IDEA: When moving into a placeholder from the end, keep the caret at the end so backspace feels more natural

[prowriting]

Currently if you backspace the character immediately after a placeholder, rather than a second backspace clearing the placeholder, the caret has been moved to the start of the placeholder and so the backspace deletes whatever is BEFORE the placeholder

This may require a rebuild (so should wait for test coverage). The caret being at the end of a placeholder, but it in an active state (from moving backward into it) would be new behaviour