feat: automatically resolve name from containing package.json

[nmn]

Walk tree to find package name from package.json file

This PR adds a tree walker to walk up the tree and find the nearest package.json file and use the name from that file to generate the "canonical file path" for a file.

This canonical file path is used for generating the variable names for:

1. defineVars calls within .stylex.js files
2. The debug classNames

Benefits

This change removes the need for passing in rootDir for the theming APIs to work.

Possible concerns

• I'm not sure if the current logic is safe on Windows.

Next Steps

• Add more tests
• Update the config options to make theming APIs on by default.
• Update the debug classNames to generate the data-style-src attribute instead.

[github-actions[bot]]

workflow: benchmarks/size

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

@stylexjs/scripts@0.8.0 size:compare ./size-compare.js /tmp/tmp.Fqm60yXUcS /tmp/tmp.IQRH59lFlu

Results	Base	Patch	Ratio
stylex/lib/stylex.js
· compressed	729	729	1.00
· minified	2,541	2,541	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