[stylex] Add types to exports

[necolas]

These types are currently used by React Strict DOM

Needed for react/react-strict-dom#311

[github-actions]

workflow: benchmarks/perf

Comparison of performance test results, measured in operations per second. Larger is better.

benchmarks@0.13.0 compare
node ./compare.js /tmp/tmp.L6OKalLN6K /tmp/tmp.X1CvrSXxn9

Results	Base	Patch	Ratio
babel-plugin: stylex.create
· basic create	538	541	1.01	+
· complex create	197	181	0.92	!!
babel-plugin: stylex.createTheme
· basic themes	466	461	0.99	-
· complex themes	43	43	1.00

[github-actions]

workflow: benchmarks/size

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

benchmarks@0.13.0 compare
node ./compare.js /tmp/tmp.bsLAy5Xsdo /tmp/tmp.1lBdqGD9o8

Results	Base	Patch	Ratio
@stylexjs/stylex/lib/cjs/stylex.js
· compressed	1,200	1,200	1.00
· minified	3,513	3,513	1.00
@stylexjs/stylex/lib/cjs/inject.js
· compressed	1,227	1,227	1.00
· minified	3,224	3,224	1.00
benchmarks/size/.build/bundle.js
· compressed	537,611	537,611	1.00
· minified	7,435,904	7,435,904	1.00
benchmarks/size/.build/stylex.css
· compressed	100,509	100,509	1.00
· minified	754,513	754,513	1.00