Fix strict transform array element type

[Boulea7]

Summary:

Fixes #53899.

MergeUnion made every transform key optional before MaximumOneOf selected a key. Indexing that optional mapped type added undefined to each element of ViewStyle['transform'] under strict null checks. This makes the intermediate keys required, preserving the existing one-key transform constraint while keeping undefined out of the array element type.

Changelog:

[General] [Fixed] - Prevent strict transform array element types from including undefined

Test Plan:

Validated after merging main at 024d5dafd530412efe43c9c2f95c9da109f48092:

• yarn build-types and yarn build-types --validate — passed; the generated snapshot is up to date.
• yarn test-generated-typescript and yarn test-typescript-legacy — passed.
• Focused ESLint and Prettier checks on _TransformStyle.js, plus git diff --check — passed.

The existing TypeScript suites use strict: false, so the strict-null behavior was checked separately through the generated public ViewStyle type. The probe below fails on unmodified 024d5daf with TS2769 at Object.keys(element) and passes on this branch. Both runs rebuilt and resolved their own generated workspace types.

After generating types, this command reproduces the check and removes its temporary file and directory:

(
  set -e
  rn_probe_dir=$(mktemp -d packages/react-native/__typetests__/.rn-transform-probe.XXXXXX)
  trap 'rm -f -- "$rn_probe_dir/transform-probe.ts"; rmdir -- "$rn_probe_dir"' EXIT
  cat > "$rn_probe_dir/transform-probe.ts" <<'TS'
import type {ViewStyle} from 'react-native';

type TransformArray = Exclude<NonNullable<ViewStyle['transform']>, string>;
const transforms: TransformArray = [{translateX: 1}];
transforms.map(element => Object.keys(element));
TS
  ./node_modules/.bin/tsc --noEmit --strict --skipLibCheck --moduleResolution bundler --module esnext --target es2020 "$rn_probe_dir/transform-probe.ts"
)

Separate strict probes passed for single-key objects, readonly arrays, animated values, string transforms, an omitted transform, and the existing optional selected property. Negative probes confirmed rejection of undefined array elements and objects with multiple transform keys.

No additional test script or strict TypeScript configuration is included, as requested in review. The generator Jest suite, Flow check, full repository lint/Jest, native builds, and RNTester were not run for this update.

Codex was used for this update and its validation.

[github-actions]

Warning

JavaScript API change detected

This PR commits an update to ReactNativeApi.d.ts, indicating a change to React Native's public JavaScript API.

• Please include a clear changelog message.
• This change will be subject to additional review.

This change was flagged as: POTENTIALLY_BREAKING

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