Bump flow to latest version and fix errors

[SamChou19815]

I want to eliminate all the remaining legacy syntax and types in this repo. But first, we need to bump to a newer version of Flow that allows modern TS like syntax. This is the PR that does it.

[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/web/index.js
· compressed	3,251	3,251	1.00
· minified	10,375	10,375	1.00
react-strict-dom/dist/web/runtime.js
· compressed	1,645	1,645	1.00
· minified	4,131	4,131	1.00
react-strict-dom/dist/native/index.js
· compressed	16,580	16,580	1.00
· minified	64,168	64,168	1.00
react-strict-animated/dist/web/index.js
· compressed	6,861	6,861	1.00
· minified	23,486	23,486	1.00
react-strict-animated/dist/native/index.js
· compressed	797	797	1.00
· minified	2,518	2,518	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	1,119,108	1,124,081	1.00	+
· small with units	491,049	484,047	0.99	-
· small with variables	670,853	682,302	1.02	+
· several small	351,096	345,821	0.98	-
· large	196,951	195,121	0.99	-
· large with polyfills	145,345	145,381	1.00	+
· complex	100,769	101,473	1.01	+
· unsupported	207,157	208,943	1.01	+
css.createTheme
· simple theme	227,642	228,638	1.00	+
· polyfill theme	213,810	214,988	1.01	+