Feature: for newly created prompt key-up deletes whole text

Problem

On Mac, when you typed a very long multiline prompt, you usually expect that key-up only switch line for cursor

Instead of this the actual behavior is as follows:

• codewhale forgets what was actually typed by user
• codewhale shows the previous command

If the typed prompt was big enough, it is rather painful to understand that you need to remember it all and retype again

Proposed solution

For if:

• there is a not empty prompt or comand in a composer
• composer contains several lines of text (and not just one)
• cursor is not on the topmost line then instead of switching to prevoius entered message cursor just jumps 1 line up

Use case

In every big enought prompt it will be useful The same is actual also for key-down

Alternatives considered

Current behavior deletes un-entered message

Impact

Rather painful message deletion