Avoid cloning nodes and clunky tests by passing pasted HTML string

[ellatrix]

No description provided.

[codecov]

Codecov Report

Merging #2479 into master will increase coverage by 0.13%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master    #2479      +/-   ##
==========================================
+ Coverage   26.88%   27.01%   +0.13%     
==========================================
  Files         158      159       +1     
  Lines        4892     5086     +194     
  Branches      814      870      +56     
==========================================
+ Hits         1315     1374      +59     
- Misses       3034     3131      +97     
- Partials      543      581      +38

Impacted Files	Coverage Δ
blocks/editable/index.js	11.06% <0%> (-0.05%)	⬇️
blocks/api/paste/strip-attributes.js	100% <100%> (ø)	⬆️
blocks/api/paste/index.js	100% <100%> (ø)	⬆️
blocks/api/paste/strip-wrappers.js	100% <100%> (ø)	⬆️
blocks/api/paste/normalise-blocks.js	96.87% <100%> (+0.2%)	⬆️
editor/header/saved-state/index.js	75% <0%> (-10.72%)	⬇️
blocks/library/heading/index.js	18.91% <0%> (-4.9%)	⬇️
editor/modes/visual-editor/block.js	0% <0%> (ø)	⬆️
blocks/inspector-controls/select-control/index.js	0% <0%> (ø)	⬆️
blocks/color-palette/index.js	0% <0%> (ø)	⬆️
... and 5 more

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[ellatrix]

Merging so we can move on with other paste PRs. This should simplify adding paste filters and tests.