[eslint-plugin] Support importSources object syntax in validImports

[necolas]

Rebase of #569

[github-actions]

workflow: benchmarks/perf

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

benchmarks@0.12.0 compare
node ./compare.js /tmp/tmp.3MwIDA1Srw /tmp/tmp.gkvN8cYmbS

Results	Base	Patch	Ratio
babel-plugin: stylex.create
· basic create	541	536	0.99	-
· complex create	186	197	1.06	!!
babel-plugin: stylex.createTheme
· basic themes	460	457	0.99	-
· complex themes	42	42	1.00

[github-actions]

workflow: benchmarks/size

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

benchmarks@0.12.0 compare
node ./compare.js /tmp/tmp.fHou949CXG /tmp/tmp.TTyvfduFci

Results	Base	Patch	Ratio
stylex/lib/cjs/stylex.js
· compressed	1,172	1,172	1.00
· minified	3,395	3,395	1.00
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