Add TypeScript types for TextEncoder/TextDecoder to global type declarations

[deyaaeldeen]

Hey! Both TextEncoder and TextDecoder are now natively available in Hermes:

• TextEncoder landed in Hermes for RN 0.74 (using TextEncoder with hermes hermes#948)
• TextDecoder landed in Dec 2025 (Add support for TextDecoder hermes#1855), should ship with RN 0.85

But neither is declared in React Native's TypeScript globals (src/types/globals.d.ts), so TypeScript users have to either cast through any, pull in lib: ["dom"], or add their own declarations to use these APIs without type errors.

Would be great to add the type declarations now that the runtime support is there. Happy to submit a PR if that helps.

[react-native-bot]

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