fix: conditional classes for dynamic styles for legacy expanded prope…

[nmn]

Fixes for dynamic styles for expanded shorthands (when using "legacy-expand-shorthands")

Work so far

In the previous two PRs, I made it so that when using a dynamic style, if the dynamic value resolves to null or undefined, then:

• Neither the inline style setting the CSS variable should be applied
• Nor the className that uses that variable should be applied.

In order words, a dynamic style that resolves to null should behave just like a regular style that resolves to null.

What was fixed

Until the previous diff, when using styleResolution: 'legacy-expand-shorthands' any dynamic styles set to a shorthand were not correctly handled. This is because the keys in the original style object, the inline styles and the applied styles did not match.

This PR fixes that by re-using the same logic used to expand keys to also expand which keys we know are dynamic.

Also completed

~~We're not correctly adding px units for all properties that only take lengths and not numbers. Specifically, shorthand properties such as margin are not handled correctly. This will be fixed next.~~

• [x] Done.

~~Also, once these PRs land, we can change the var(--prop-name, revert) to just var(--prop-name) as the static values used for dynamic styles.~~

• [x] Done

[github-actions[bot]]

workflow: benchmarks/size

Comparison of minified (terser) and compressed (brotli) size results, measured in bytes. Smaller is better.

@stylexjs/[email protected] size:compare ./size-compare.js /tmp/tmp.l3yBN3muHu /tmp/tmp.KIvZnKOrKP

Results	Base	Patch	Ratio
stylex/lib/stylex.js
· compressed	899	899	1.00
· minified	3,223	3,223	1.00
stylex/lib/StyleXSheet.js
· compressed	1,266	1,266	1.00
· minified	3,776	3,776	1.00
rollup-example/.build/bundle.js
· compressed	563,025	563,025	1.00
· minified	10,185,368	10,185,368	1.00
rollup-example/.build/stylex.css
· compressed	99,154	99,154	1.00
· minified	745,649	745,649	1.00