Right-Click: Add options to cut/copy/paste blocks

[swissspidy]

As outlined in #2785, let's extend the block settings menu to offer cut + copy options, where the block content is added to the clipboard.

Cases where Gutenberg is adding blocks to the clipboard:

https://github.com/WordPress/gutenberg/blob/b95e865de32ee62d722be3e3e71b334a4b639032/packages/block-editor/src/components/copy-handler/index.js#L26-L57

https://github.com/WordPress/gutenberg/blob/b95e865de32ee62d722be3e3e71b334a4b639032/packages/components/src/clipboard-button/index.js#L27-L67

Pasting would be handled by the RichText component which we use in all the text-based blocks and has some complex logic for handling the clipboard data properly:

https://github.com/WordPress/gutenberg/blob/03121c5e59c63d4c79a293f71bbb7b9613fd311c/packages/rich-text/src/component/index.js#L187-L260

We probably need to copy most of that component's logic.

[westonruter]

Special care will be needed for paste since access is restricted for security/privacy reasons. See https://developers.google.com/web/updates/2018/03/clipboardapi

[spacedmonkey]

Testing details.

User could be able to do the copying.

1. Copy / cut a block using a keyboard shortcuts crt + c / crt x
2. Select a block, right click, copy / cut using custom popover menu and not standard OS level context menu.
3. Blocks can be pasted using keyboard shortcut.
4. Blocks can be pasted using right context menu.
5. Block should be able to be pasted multiple times.
6. When blocks are pasted, they should be pasted where the cursor was placed.
7. Blocks can be removed using the context menu.
8. Blocks can be duplicated using the context menu.
9. Blocks should able to be pasted on another amp page.
10. Call to action and attachment block, shouldn't be able to copied.

To test this, a test script that mixes and matches elements of this list should be created. An example would be, copy a block using keyboard and paste using the context menu.

[csossi]

• "cut" works fine on right-click menu, but the keyboard ctrl-x doesn't remove the original selection (works the same as keyboard ctrl-c)
• am able to copy CTA blocks

[spacedmonkey]

• am able to copy CTA blocks

You should be able to copy a CTA block. I can't paste it in the same page, as you can only have one CTA per page. But you can copy and paste a CTA onto another page if you want.

[spacedmonkey]

The cut via keyboard fix has now been merged. See #3231

[csossi]

Some odd behaviour when ctrl-x/cutting a CTA

• add a page 2 to a story
• add a text block
• add a CTA
• add a page 3, so you have something like this:
  
• ctrl-x on the CTA on page 2
• ctrl-v on page 3

I ended up with (text got copied over instead):

[csossi]

Verified in QA

[spacedmonkey]

Screencast can be found here - https://www.youtube.com/watch?v=47onOiC-EhU&feature=youtu.be