[eslint-plugin] Add flexFlow shorthand expansion to stylex-valid-shorthands

[abhakat]

Expand flexFlow shorthand into flexDirection + flexWrap longhands. Both tokens are
validated against keyword sets before applying the fix, preventing incorrect expansions
for invalid values.

Stack: 5/7 — depends on #1588

What changed / motivation ?

• flexFlow: 'row wrap' → flexDirection: 'row' + flexWrap: 'wrap'
• flexFlow: 'wrap column' → flexDirection: 'column' + flexWrap: 'wrap' (order-independent)
• flexFlow: 'row banana' → error with no autofix (invalid wrap token)
• Single values pass through unchanged

Linked PR/Issues

Follow-up to #1537

Additional Context

Added tests covering: single-value passthrough, direction+wrap expansion, reversed token order,
invalid tokens (CANNOT_FIX), column-reverse/nowrap.

Pre-flight checklist

• I have read the contributing guidelines
  Contribution Guidelines
• Performed a self-review of my code

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
stylex	Skipped		Apr 6, 2026 9:55pm

[github-actions]

workflow: benchmarks/perf

Comparison of performance test results, measured in operations per second. Larger is better.
yarn workspace v1.22.22
yarn run v1.22.22
$ node ./compare.js /tmp/tmp.aMlpEFSEa4 /tmp/tmp.0lOsXYXvOy

Results	Base	Patch	Ratio
babel-plugin: stylex.create
· basic create	523	529	1.01	+
· complex create	67	66	0.99	-
babel-plugin: stylex.createTheme
· basic themes	435	434	1.00	-
· complex themes	35	35	1.00
Done in 0.08s.
Done in 0.32s.

[github-actions]

workflow: benchmarks/size

Comparison of minified (terser) and compressed (brotli) size results, measured in bytes. Smaller is better.
yarn workspace v1.22.22
yarn run v1.22.22
$ node ./compare.js /tmp/tmp.iQzs1Lg6Sf /tmp/tmp.L5x1Nqe6T2

Results	Base	Patch	Ratio
@stylexjs/stylex/lib/cjs/stylex.js
· compressed	1,441	1,441	1.00
· minified	4,386	4,386	1.00
@stylexjs/stylex/lib/cjs/inject.js
· compressed	1,793	1,793	1.00
· minified	4,915	4,915	1.00
benchmarks/size/.build/bundle.js
· compressed	496,650	496,650	1.00
· minified	4,847,840	4,847,840	1.00
benchmarks/size/.build/stylex.css
· compressed	99,653	99,653	1.00
· minified	747,850	747,850	1.00
Done in 0.08s.
Done in 0.30s.