Add background-origin utilities

[davidluhr]

This PR adds support for the background-origin property.

An example use case is a button with a gradient background and transparent border. This typically results in unexpected border colors appearing, but can be fixed with background-origin: border-box; in CSS (or bg-origin-border in Tailwind CSS with this PR).

Here's the API:

Class	CSS
bg-origin-border	background-origin: border-box
bg-origin-padding	background-origin: padding-box
bg-origin-content	background-origin: content-box

Only responsive variants are enabled by default, but can be configured under the backgroundOrigin key in your tailwind.config.js file.

[codecov-commenter]

Codecov Report

Merging #4117 (8a39fae) into master (6ed835c) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head 8a39fae differs from pull request most recent head 3c39ff8. Consider uploading reports for the commit 3c39ff8 to get more accurate results

@@            Coverage Diff             @@
##           master    #4117      +/-   ##
==========================================
+ Coverage   86.82%   86.84%   +0.02%     
==========================================
  Files         339      341       +2     
  Lines        4826     4835       +9     
  Branches      919      919              
==========================================
+ Hits         4190     4199       +9     
  Misses        561      561              
  Partials       75       75              

Impacted Files	Coverage Δ
jit/corePlugins/index.js	90.32% <ø> (ø)
src/corePluginList.js	100.00% <ø> (ø)
stubs/defaultConfig.stub.js	100.00% <ø> (ø)
jit/corePlugins/backgroundOrigin.js	100.00% <100.00%> (ø)
src/plugins/backgroundOrigin.js	100.00% <100.00%> (ø)

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[adamwathan]

Well done Mr. Luhr, well done.