use calculateSelectorNode for calculating specificity

[bartveneman]

refs #422

[codecov-commenter]

Bundle Report

Changes will increase total bundle size by 167.34kB ⬆️

Bundle name	Size	Change
analyzeCss-analyzeCss-esm	99.27kB	99.27kB ⬆️
analyzeCss-analyzeCss-esm-analyzeCss-umd	68.07kB	68.07kB ⬆️

[codspeed-hq]

CodSpeed Performance Report

Merging #423 will improve performances by 50.23%

_{Comparing perf/calculate-selector-node (4fd5f5b) with master (bc42b86)}

Summary

⚡ 5 improvements
✅ 2 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	perf/calculate-selector-node	Change
⚡	color names	859.5 µs	572.6 µs	+50.12%
⚡	font shorthand	545.9 µs	458.2 µs	+19.14%
⚡	high complexity/specificity selectors	1,016.6 µs	676.7 µs	+50.23%
⚡	slice of Syntax.fm	6.5 ms	5.2 ms	+24.43%
⚡	slice of nerdy.dev	9 ms	6.9 ms	+30.44%

[bartveneman]

superseded by #444