Avoid allocations in Animated string interpolation

[shubh73]

Summary:

createStringInterpolation (string and color outputRanges) allocated two arrays and a closure on every call: interpolations.map(...), then components.map(...).join(''), or a .map in the rgba branch. This runs every frame for JS-driven animations.

This builds the string with a plain loop and computes r/g/b/a as locals. Output is unchanged: I compared 1,442 results (colors, units, negatives, NaN/-0, all extrapolate modes) from before and after the change, and they match exactly.

Hermes via Fantom, 1M calls per sample.

Time (median of 5 runs)

Output range	Before	After	Change
'0deg' → '360deg'	876 ms	704 ms	-20%
'0px 0px 0px' → '-10.5px 20px 4px'	1931 ms	1734 ms	-10%
'#FF9500' → 'rgba(50, 150, 250, 0.4)'	1577 ms	1337 ms	-15%

Memory (from HermesInternal.getInstrumentedStats(), identical across runs)

Output range	Allocated per call	GCs per 1M calls
'0deg' → '360deg'	901 B → 590 B (-35%)	221 → 145
'0px 0px 0px' → '-10.5px 20px 4px'	1822 B → 1407 B (-23%)	443 → 342
'#FF9500' → 'rgba(50, 150, 250, 0.4)'	1831 B → 1543 B (-16%)	445 → 375

Time ranges (min–max per run median)

Output range	Before	After
'0deg' → '360deg'	873–879 ms	697–780 ms
'0px 0px 0px' → '-10.5px 20px 4px'	1924–1951 ms	1701–2577 ms (one noisy run)
'#FF9500' → 'rgba(50, 150, 250, 0.4)'	1572–1590 ms	1309–1343 ms

Node/V8 shows the same direction (-29% / -12.5% / -3.9%).

Changelog:

[GENERAL] [CHANGED] - Avoid per-call allocations in Animated string and color interpolation

Test Plan:

• yarn fantom packages/react-native/Libraries/Animated/__tests__/Interpolation-itest.js: 35 passed (added cases for multiple numeric components and prefix/suffix)
• yarn fantom packages/react-native/Libraries/Animated: 302 passed
• yarn test packages/react-native/Libraries/Animated: 65 passed
• yarn flow-check, yarn lint, yarn format-check-javascript: clean
• Benchmark: FANTOM_RUN_BENCHMARKS=1 yarn fantom packages/react-native/Libraries/Animated/__tests__/AnimatedInterpolation-benchmark-itest.js. OSS can't run opt mode, so I ran it with @fantom_native_opt false, @fantom_js_opt true, @fantom_js_bytecode false. Not measured on a device.

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[meta-codesync]

@fabriziocucci has imported this pull request. If you are a Meta employee, you can view this in D122044561.

[meta-codesync]

@fabriziocucci merged this pull request in efc5161.