feat: add TextEncoder/TextDecoder scene globals

[kuruk-mm]

Scene runtimes have no TextEncoder/TextDecoder because the embedded deno_core runs without deno_web, so SDK scenes and libraries relying on the WHATWG text codecs crash at load (or fall back to slow bundled polyfills).

This adds two std-only ops (op_utf8_encode/op_utf8_decode) and a small JS shim module registered like the existing fetch/ws shims, installing WHATWG-shaped TextEncoder and TextDecoder on globalThis when absent.

• TextDecoder accepts the WHATWG utf-8 label set with fatal and ignoreBOM support, throws RangeError for any other encoding and a loud TypeError for the unsupported { stream: true } option.
• TextEncoder implements encode and encodeInto, including correct UTF-8 boundary truncation for encodeInto on short destinations.
• Decoding uses Rust's from_utf8_lossy, whose maximal-subparts U+FFFD substitution matches the WHATWG spec exactly; encoding inherits USVString lone-surrogate replacement from deno_core's string conversion. No new dependencies.

Unit tests cover the Rust decode paths (cargo test text_encoding) and the JS shim (13 node:test cases mirroring ws.test.cjs). Full crate suite passes (170 tests), cargo fmt clean. The ops are pure std string/slice operations with no OS APIs, so this ships identically on desktop and the Android/iOS builds (default features include use_deno on all targets).

Scenes built with the current SDK keep working unchanged: the SDK installs its polyfill only when the global is absent, so the native-backed implementation wins automatically, including for already-published content.

Related: decentraland/js-sdk-toolchain#1452 (slims the SDK polyfill to a validating utf-8 codec), decentraland/bevy-explorer#958 (same exposure via deno_web).

Note for maintainers: the shim tests are runnable with node --test lib/src/dcl/js/js_modules/text_encoding.test.cjs and are meant to join ws.test.cjs in the static-checks node --test step; that one-line workflow edit is left out of this PR (pushed from a token without workflow scope).

Supersedes #2517 (same changes, re-committed with a signed commit).

[github-actions]

📦 Build Report

🤖 Android

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APK	📱 Download APK
AAB	main/release builds only
Debug Symbols	main/release builds only

Build Status: ✅ Success

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🔄 Updated: 2026-07-15 00:13:41 UTC