Fix down arrow key not working after font size change

[objectiveous]

Description

After changing the font size, the down/up arrow keys stop moving the cursor across line boundaries. The root cause is that TextViewLayoutManager caches an estimated line height that isn't invalidated when the font changes. The moveDown:/moveUp: methods use this stale value to calculate the target point, which lands within the same line instead of the next one.

Fix:

• Re-assign renderDelegate on the layout manager after font or line height multiplier changes, which forces the cached estimate to refresh.
• Add explicit handleArrowKey dispatch so arrow keys with all modifier combinations (Shift, Option, Cmd) are handled correctly when the local event monitor intercepts them.
• Add Control-N / Control-P support for Emacs-style vertical movement.

Related Issues

• Related to cursor navigation after configuration changes

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code