Use postcss to extract styles in Expo example

[necolas]

Extract styles to static CSS using postcss, as there is no existing Metro integration.

Fix #34
Ref #236

[github-actions]

workflow: benchmarks/size

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

Results	Base	Patch	Ratio
react-strict-dom/dist/dom/index.js
· compressed	2,495	2,515	1.01	+
· minified	8,686	8,688	1.00	+
react-strict-dom/dist/dom/runtime.js
· compressed	855	855	1.00
· minified	2,433	2,435	1.00	+
react-strict-dom/dist/native/index.js
· compressed	15,824	15,824	1.00
· minified	59,086	59,086	1.00

[github-actions]

workflow: benchmarks/perf (native)

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

Results	Base	Patch	Ratio
css.create
· small	1,154,662	1,167,428	1.01	+
· small with units	452,014	454,353	1.01	+
· small with variables	684,356	691,427	1.01	+
· several small	328,871	326,277	0.99	-
· large	213,974	213,474	1.00	-
· large with polyfills	149,248	150,159	1.01	+
· complex	101,737	102,335	1.01	+
· unsupported	224,149	221,856	0.99	-
css.createTheme
· simple theme	223,441	225,295	1.01	+
· polyfill theme	210,222	210,494	1.00	+
css.props
· small	246,739	246,158	1.00	-
· small with units	193,540	193,032	1.00	-
· small with variables	106,469	105,751	0.99	-
· small with variables of units	74,921	75,236	1.00	+
· large	104,618	104,339	1.00	-
· large with polyfills	37,447	37,752	1.01	+
· complex	24,099	24,291	1.01	+
· unsupported	153,062	148,315	0.97	-
· simple merge	164,192	164,064	1.00	-
· wide merge	18,323	18,301	1.00	-
· deep merge	17,953	18,005	1.00	+
· themed merge	32,912	32,985	1.00	+

[necolas]

Thanks @javascripter for the quick patches! LGTM now. Let me know what you think

[javascripter]

@necolas Thanks for testing out. Looks good to me as well!