Polyfill experimental 'spring()' timing function for native

[necolas]

Uses React Native Animated API to polyfill a 2016 proposal for the spring() timing function in CSS.

https://lists.w3.org/Archives/Public/www-style/2016Jun/0181.html

[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	2,513	2,513	1.00
· minified	8,695	8,695	1.00
react-strict-dom/dist/dom/runtime.js
· compressed	855	855	1.00
· minified	2,435	2,435	1.00
react-strict-dom/dist/native/index.js
· compressed	16,028	16,226	1.01	+
· minified	59,946	60,854	1.02	+

[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	1,151,573	1,148,999	1.00	-
· small with units	438,627	433,871	0.99	-
· small with variables	677,724	662,277	0.98	-
· several small	322,634	323,201	1.00	+
· large	209,089	209,772	1.00	+
· large with polyfills	147,657	146,729	0.99	-
· complex	101,217	100,531	0.99	-
· unsupported	221,266	221,305	1.00	+
css.createTheme
· simple theme	231,069	231,913	1.00	+
· polyfill theme	215,034	217,313	1.01	+
css.props
· small	244,811	244,243	1.00	-
· small with units	191,417	191,271	1.00	-
· small with variables	106,561	106,396	1.00	-
· small with variables of units	75,582	74,890	0.99	-
· large	104,775	102,610	0.98	-
· large with polyfills	37,503	37,374	1.00	-
· complex	23,601	23,529	1.00	-
· unsupported	147,457	139,584	0.95	!!
· simple merge	163,107	162,411	1.00	-
· wide merge	17,905	17,931	1.00	+
· deep merge	17,583	17,509	1.00	-
· themed merge	31,240	31,503	1.01	+