Rework selection inclusion; new Send button UX

[dlqqq]

Description

• Removes "Include selection" checkbox, and replaces it with an alternative UI
• Implements a new send button with a dropdown button to the right.
  • When this button is clicked, it opens a menu containing an option with the label "Send message with selection (X lines / 1 active cell selected)".
  • This option is disabled if there is no text selection or active cell.
  • When a text selection is made within the active cell, it takes precedence over the active cell. This allows users to only include a selected range within an active cell.
  • When /fix is the current slash command, "Send message with selection" does the same thing as the default "Send message" button, since both of them should always include a code cell w/ error output when /fix is being called.
• This feature allows users to include a selection with their prompt just once, instead of having selection inclusion be a feature that is enabled until explicitly disabled.
• Fixes Remove "Include selection" checkbox #864.

Demo

Screen.Recording.2024-07-23.at.10.49.29.AM.mov

[JasonWeill]

Can you please update the text and screenshots in the user docs to reflect this new UI?

[dlqqq]

Since this is a fairly significant change to the UX, I'm leaving this PR open for a few more days to allow other contributors to review, test, and offer feedback here.

@JasonWeill I'll update the docs after this PR is approved and merged, since the UI may change as others offer feedback.

[JasonWeill]

The code and UI look great! I noticed that I can use TAB to get to the caret:

… but when I press ENTER, instead of opening the menu, the prompt gets sent without the selection. Pressing SPACE causes the menu to appear, though. Not sure if we can override this, and it's a pretty minor annoyance.

[krassowski]

👍 For context, on GitHub pressing either Enter or Space with focus on the caret does open the menu.

[dlqqq]

All comments addressed! This PR is ready for another round of review.

@JasonWeill I've just pushed a commit that allows the Send button dropdown menu to be opened with either the Space or Enter key. Thanks for catching that! 👍

[JasonWeill]

When I use the keyboard to enter a prompt, TAB over to the dropdown arrow, press ENTER to open the menu, and then press ⬇️ and ENTER to send the message with the selection, it looks like the message is sent twice, once with the selection attached and once without.

[dlqqq]

@JasonWeill Good catch, thanks! Fixed in the latest revision.

Screen.Recording.2024-07-29.at.2.29.41.PM.mov

[JasonWeill]

Now, if I type a prompt foo, tab over to the dropdown, and press ENTER once, the menu appears, with nothing selected. When I press ENTER a second time, the prompt is sent without the selection, but the menu continues to appear. It seems like the sole menu item should be selected by default, or sending a message should close the menu if it's open.

[dlqqq]

@JasonWeill OK, I've re-enabled auto focusing for the first item. I had it disabled because I thought it looked ugly, but I'm willing to re-enable it for keyboard accessibility.