Improved arbitrary calc support for CSS variables

[sibbng]

Hi, this PR does 2 things:

• Prevent adding space to dashy css variables
• Allows calc functions as fallback value of css variables (or anywhere in arbitrary values)

Classes for testing:

/* test */
"w-[calc(var(--width-10px,calc(-20px-(-30px--40px)))-50px)]";
/* expected */
width: calc(var(--width-10px,calc(-20px - (-30px - -40px))) - 50px)
/* without this pr */
width: calc(var(--width - 10px,calc(-20px - (-30px - -40px))) - 50px)

/* test */
"w-[var(--width-10px,calc(-20px-(-30px--40px)))]";
/* expected */
width: var(--width-10px,calc(-20px - (-30px - -40px)))
/* without this pr */
width: var(--width-10px,calc(-20px-(-30px--40px)))

I didn't read source code very carefully and didn't clone this repo to my local machine yet to run tests. I would be happy to update tests if required but I didn't find any clear documentation how to run jit tests properly. Cloning tailwind-jit repo was an option but I didn't want to go for it now. I thought asking for it here would be better.

[codecov-io]

Codecov Report

Merging #3933 (0848bdf) into master (38661c3) will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3933      +/-   ##
==========================================
- Coverage   86.90%   86.80%   -0.11%     
==========================================
  Files         319      339      +20     
  Lines        4277     4819     +542     
  Branches      788      918     +130     
==========================================
+ Hits         3717     4183     +466     
- Misses        485      561      +76     
  Partials       75       75              

Impacted Files	Coverage Δ
jit/pluginUtils.js	93.13% <100.00%> (ø)
stubs/defaultConfig.stub.js	100.00% <0.00%> (ø)
src/plugins/backdropInvert.js	85.18% <0.00%> (ø)
src/plugins/filter.js	100.00% <0.00%> (ø)
src/plugins/backdropHueRotate.js	85.18% <0.00%> (ø)
src/plugins/blur.js	86.20% <0.00%> (ø)
src/plugins/backdropSepia.js	85.18% <0.00%> (ø)
src/plugins/sepia.js	84.37% <0.00%> (ø)
src/plugins/backdropSaturate.js	85.18% <0.00%> (ø)
src/plugins/backdropOpacity.js	85.18% <0.00%> (ø)
... and 12 more

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[sibbng]

Closing in favor of #4147