Better inline paste

[ellatrix]

Fixes #2459, and inline Editable paste.

• The pasteHandler now really handles all paste. Before, the Editable component handled block paste and inline paste.
• We pass { inline: true } if the editable expects inline content. If so, we strip everything that is not text or inline tags.
• Images are now seen as non inline content, so a block will be created.

To test:

• Copy an image from the old editor (click, copy), then paste it in a paragraph. An image block should be created.
• Copy some content that is not all inline. This can be some blocks, or some content from a site. Paste it in a caption or another single line Editable. The content should be pasted in the caption, but only as text and formatting.

[codecov]

Codecov Report

Merging #2497 into master will increase coverage by 2.23%.
The diff coverage is 77.46%.

@@            Coverage Diff             @@
##           master    #2497      +/-   ##
==========================================
+ Coverage    27.2%   29.44%   +2.23%     
==========================================
  Files         160      167       +7     
  Lines        4914     5203     +289     
  Branches      819      876      +57     
==========================================
+ Hits         1337     1532     +195     
- Misses       3030     3108      +78     
- Partials      547      563      +16

Impacted Files	Coverage Δ
blocks/api/paste/normalise-blocks.js	96.66% <100%> (-0.21%)	⬇️
blocks/api/paste/utils.js	100% <100%> (ø)
blocks/api/paste/create-unwrapper.js	100% <100%> (ø)
blocks/api/paste/is-inline-content.js	100% <100%> (ø)
blocks/api/paste/comment-remover.js	100% <100%> (ø)
blocks/api/paste/strip-attributes.js	100% <100%> (ø)	⬆️
blocks/api/paste/index.js	78.57% <57.14%> (-21.43%)	⬇️
blocks/editable/index.js	11.44% <9.09%> (+0.42%)	⬆️
blocks/library/video/index.js	25% <0%> (-5.77%)	⬇️
blocks/inspector-controls/select-control/index.js	0% <0%> (ø)	⬆️
... and 14 more

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[ellatrix]

I feel like it might be better to have one loop over all nodes and then apply filters on each node (except for normalising blocks). I'll explore that in a separate PR.

[georgeh]

[georgeh]

Good! I like the imports from window.Node better. One less piece of duplication