Add `Submit` and `SubmitOrNewline` editor events

• Submit is used to return data unconditionally. This is useful for example if you want compiler to show you where the unclosed paren that doesn't pass validation actually is.
• SubmitOrNewline is similar to Enter but inserts a new line if the cursor is not at the end of the buffer. It's useful to insert newlines in the middle of the text when editing.

This also removes unconditional KeyCode::Enter to ReedlineEvent::Enter event mapping and sets it in the keybindings normally (so you can rebind to Submit or SubmitOrNewline)

That sounds like a good idea to decouple some of that hard coded behavior on enter. I will try to take a look if there is stuff that might break. Having the option to explicitly bind it to a separate binding sounds definitely nice, weighing the options in my head of whether we should have all three or a config between the Enter and SubmitOrNewline behavior

Yes, Enter and SubmitOrNewline usually may be configurable. In Rustyline it's a bool field in enum variant. On the other hand, I don't know if it makes sense to make this variable somewhere in the EditMode, as that would require a special method to configure that (so one more thing to learn), while changing binding sounds obvious and clear to me.

Submit on the other hand has to be a separate, as we, for example, bind Submit on Alt+Return and SubmitOrNewline on Return.

Seems to work fine in my testing! Thanks for the elegant solution!

I will land it as is to allow users to play with it in the next (nushell) release. If we want to make a later breaking change we to the bindings we may bunch it up with other likely changes.