Perf: Remove runtime injection from runtime

[nmn]

What changed / motivation ?

The inject function has been removed from the main export of @stylex/stylex. Now the inject function can only be used by manually importing @stylex/stylex/lib/stylex-inject.

The Babel plugin has similarly been updated to import the inject function from the new location when runtimeInjection is turned on.

Also, runtimeInjection now accepts a string or {from: string, as: string} object to be able to override the inject function module location.

Additional Context

Tests have been updated to reflect the changes. The updated snapshots will show what has changed.

NOTE: The Webpack plugin is currently inlining the stylex-inject module in the generated code in the snapshot test. Trying to configure Webpack to not do that is causing strange errors.

Pre-flight checklist

• Performed a self-review of my code

[github-actions]

compressed-size: runtime library

Size change: -0.07 kB
Total size: 2.29 kB

Filename: gzip (minify)	kB size	kB change	% change
./packages/stylex/lib/stylex.js	0.95 (3.31)	-0.07 (-0.22)	-7.0% (-6.3%)	🟢

View unchanged

Filename: gzip (minify)	kB size	kB change	% change
./packages/stylex/lib/StyleXSheet.js	1.34 (3.41)	0.00 (0.00)	0.0% (0.0%)

[github-actions]

compressed-size: e2e bundles

Size change: 0.00 kB
Total size: 1122.94 kB

View unchanged

Filename: gzip (minify)	kB size	kB change	% change
./apps/rollup-example/.build/bundle.js	998.63 (9939.85)	0.00 (0.00)	0.0% (0.0%)
./apps/rollup-example/.build/stylex.css	124.30 (874.43)	0.00 (0.00)	0.0% (0.0%)

[necolas]

We should probably be checking the size of the bundled runtime in the CI task. It hasn't been showing the contribution of inject or styleq, so the size savings aren't showing up in the results

[nmn]

We should probably be checking the size of the bundled runtime in the CI task

I am looking into that. The numbers above are by using browserify, terser and gzip. I expect using rollup might squeeze this down a bit more.

[necolas]

oh actually it looks like styleq is inlined in lib/stylex.js, so we're good. the CI workflow already minifies and gzips.

[necolas]

The webpack snapshot issue is because externals doesn't work on generated code, only source code. I looked into a bunch of potential alternatives, but nothing seems to work or doesn't support ESM syntax. Just a shortcoming of webpack

[nmn]

2.29 kB

This is in the ballpark of the size I got in local testing, but the comparison is still wrong since this PR cut the size in half.

Will figure this out later.

[necolas]

It's just because we don't inline ./stylex/lib/StyleXSheet.js into the main export of the package - the size of that file is listed separately in the "unchanged" files table. If we had size-diffed a production rollup bundle, we'd have seen the 3K reduction from inject not being imported anymore.