feat: use dedicated events for buffer jumps while preserving selection via EditCommands

[Juhan280]

This adds new ReedlineEvent variants for moving to the start and end of the buffer. These are added alongside existing EditCommands to provide a more direct way to trigger these movements. These were added to allow traversing the history after moving the cursor the start or end of the buffer.

The default Emacs and Vi keybindings have been updated to use them. But in visual mode, we are still using the EditCommand variants.

[Juhan280]

If you have suggestions for more better enum variant name or doc, please share.

Also in src/edit_mode/vi/motion.rs, there are todo comments for Motion::Up and Motion::Down arm of the to_reedline method. If what have I done so far makes sense, I can also add their EditCommand variants to make them work in visual mode