Replace React utility types with $ with the namespaced ones

[SamChou19815]

One day, Flow will delete React$MixedElement, React$Node and all other dollar types from the global libdef, since they are considered to be internal. All these react utility types can already be used without importing React so there is no practical benefit of keeping these dollar types either.

[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	2,488	2,488	1.00
· minified	8,586	8,586	1.00
react-strict-dom/dist/dom/runtime.js
· compressed	850	850	1.00
· minified	2,404	2,404	1.00
react-strict-dom/dist/native/index.js
· compressed	15,651	15,651	1.00
· minified	58,387	58,387	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	1,130,847	1,149,187	1.02	+
· small with units	449,763	452,137	1.01	+
· small with variables	684,939	681,937	1.00	-
· several small	329,191	330,143	1.00	+
· large	214,591	215,842	1.01	+
· large with polyfills	150,305	149,182	0.99	-
· complex	103,080	102,001	0.99	-
· unsupported	224,090	223,849	1.00	-
css.createTheme
· simple theme	222,113	221,481	1.00	-
· polyfill theme	208,422	209,179	1.00	+
css.props
· small	249,412	249,339	1.00	-
· small with units	192,623	194,878	1.01	+
· small with variables	106,626	107,510	1.01	+
· small with variables of units	75,758	76,304	1.01	+
· large	106,716	106,806	1.00	+
· large with polyfills	37,630	37,696	1.00	+
· complex	24,202	24,328	1.01	+
· unsupported	149,049	150,648	1.01	+
· simple merge	165,075	166,947	1.01	+
· wide merge	18,426	18,238	0.99	-
· deep merge	17,750	17,879	1.01	+
· themed merge	32,113	32,281	1.01	+

[necolas]

Thanks Sam