CodeEdit: Fix move lines up/down viewport and selection issues

[kitbdev]

• Fixes Script editor no longer scrolls when you move line with Alt+Up/Down #93588

Also fixes some edge cases I found when testing.

• Move lines up/down at the top/bottom when the selection ends at column 0 should not change the selection.
• Move lines up or down when a selection ends at column 0 and there is another selection on that line adjusted the selection incorrectly.
• Move lines down when a selection ends at column 0 and there is a selection on the next line adjusted the selection incorrectly.
• Added tests for these.
• Added tests for unfolding when moving lines up or down.

[akien-mga]

Thanks!