Ensure variants are grouped properly for plugins with order-dependent utilities

[adamwathan]

Fixes #4038.

Prior to this we were using multiple addUtilities calls within one plugin sometimes to make sure that certain things were guaranteed to be in a certain order in JIT mode. It turns out that wasn't even necessary because we were already counting each utility in every addUtilities call toward the total sort count, not just counting the addUtilities calls themselves.

This PR collapses anywhere where we had multiple calls, as multiple calls were resulting in variants for the first call showing up in the output before non-variant utilities for subsequent calls.

Before:

.block {
  display: block
}

@media (prefers-color-scheme: dark) {
  .dark\:block {
    display: block;
  }
}

.hidden {
  display: none;
}

After:

.block {
  display: block
}

.hidden {
  display: none;
}

@media (prefers-color-scheme: dark) {
  .dark\:block {
    display: block;
  }
}

[codecov-commenter]

Codecov Report

Merging #4273 (7eac48a) into master (e399c5f) will increase coverage by 0.02%.
The diff coverage is n/a.

❗ Current head 7eac48a differs from pull request most recent head 82c61ed. Consider uploading reports for the commit 82c61ed to get more accurate results

@@            Coverage Diff             @@
##           master    #4273      +/-   ##
==========================================
+ Coverage   71.17%   71.19%   +0.02%     
==========================================
  Files         218      218              
  Lines        4721     4715       -6     
  Branches      776      776              
==========================================
- Hits         3360     3357       -3     
+ Misses       1274     1271       -3     
  Partials       87       87              

Impacted Files	Coverage Δ
src/plugins/display.js	50.00% <ø> (ø)
src/plugins/fontVariantNumeric.js	50.00% <ø> (ø)
src/plugins/textOverflow.js	50.00% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e399c5f...82c61ed. Read the comment docs.