Add paste key

[devycarol]

This patch adds a toolbar paste key, which can be used in regular layouts. Long-clicking the toolbar key opens the clipboard history if enabled, otherwise just pastes normally. Having it as a separate key helps make what the clipboard key does more clear, and allows for easy one-tap pasting without disabling clipboard history

I've put it in all the default toolbar layouts, replacing "select all" in the main toolbar and "one handed mode" in the clipboard one. I've also reorganized them, aiming for a more coherent design pattern, but I can revert any of those things if you wish.

Many lines in ToolbarUtils.kt have been reorganized to help me navigate it moving forward.

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Progress on #357

[Helium314]

I still need a little time to decide whether I'm ok with the changed defaults. Otherwise it looks good.

[devycarol]

Happy to revert any of those, already unpinned paste from the default now that we have clipboard suggestions.

On that matter, I've also changed that suggestion icon from 'clipboard' to 'paste'. I'd really like to see that association of "paste icon = paste action centric, clipboard icon = clipboard history centric," but let me know if you want me to revert that.

[devycarol]

I'll go ahead and explain what I've tried to do with the default toolbars. Goals: be as similar to the previous default as possible, add in 'paste' since it's of about equal importance to 'copy', and improve a little on organization. For specifics,

Clipboard toolbar:

• Replace one-handed, since it's not related to pasting/editing text.
• Move clear-clipboard far left, since it's the most drastic action and should not be easy to accidentally hit—currently it's right next to the often-repeated right arrow, but I don't feel comfortable touching that key at all if it's right next to "clear history."
• Scoot 'undo' over right of the arrow keys, and then arrange undo/cut/copy/paste in the traditional "ZXCV" ordering from qwerty.
• No further changes to the right.

Main toolbar:

• Replace select-all. That key juxtaposed with select-word is visually noisy and ambiguous for those who don't look in the settings. Also, even with 'undo' available, it's somewhat volatile when bumped accidentally. You can still select all by long-clicking select-word, which is a more clear intention.
• Move 'settings' far left, it's the most drastic as it opens a whole new activity (triggering onStop for the app you're typing in, etc.) We then have 'voice' which opens a separate IME, and 'clipboard' which opens a separate layout.
• Put 'paste' to the right of 'copy', avoid further changes.

In the future, it might be a good idea to prevent sister keys like left/right and undo/redo from getting swapped by RTL.

[Helium314]

In the future, it might be a good idea to prevent sister keys like left/right and undo/redo from getting swapped by RTL.

RTL handling is something that could be improved in general. Currently iirc things depend on the main keyboard language, so arrows and swiping may use the wrong direction depending on whether there is actual RTL text or not (e.g. only numbers). When you mix LTR and RTL things can get even worse, but I'm not sure how much complexity I want to add on this.