feat: read blob bytes directly in FileReader.readAsArrayBuffer

[paradowstack]

Rebase Note:

This branch is stacked on #57937 (Promise<ArrayBuffer> for Java/ObjC TurboModules) and #58029 (feat: support Array as a TurboModule method parameter) and #58030 (feat: accept ArrayBuffer and ArrayBufferView parts in Blob and File) and must be rebased onto main once that lands. For now review only the last commit.

Summary:

FileReader.readAsArrayBuffer() was implemented on top of readAsDataURL: native base64-encoded the blob into a data URL, JS split the string and decoded it back to bytes with base64-js. That is a base64 encode, a JS decode, and two full copies of the payload for every read.

Native now returns the bytes directly. BlobModule.resolveBuffer / -[RCTBlobManager resolveBuffer:offset:size:] copy the requested range into an ArrayBuffer / RCTArrayBuffer, and readAsArrayBuffer resolves the Promise with it — zero-copy from there to JS. The single copy is required rather than incidental: the buffer is handed to JS zero-copy, and Blobs are immutable per the W3C File API, so JS must not be able to write through to blob storage.

Rebase Note:

This branch is stacked on #57937 (Promise<ArrayBuffer> for Java/ObjC TurboModules) and must be rebased onto main once that lands.

Changelog:

[GENERAL] [ADDED] - FileReader.readAsArrayBuffer() reads blob bytes directly instead of decoding a base64 data URL

Test Plan:

• FileReader-test covers a successful read, TypeError on a null blob, aborting a pending read, the stale-read guard when a newer read supersedes an in-flight one, and a NotReadableError DOMException on rejection.
• FileReaderModuleTest covers reading a whole blob, an offset/size range, an unknown blob id, a missing blob id, and that the resolved buffer does not alias blob storage.
• BlobModuleTest / RCTBlobManagerTests cover resolveBuffer for whole and ranged reads, an unknown id, and that the returned buffer is an independent copy with a full 0..capacity window.
• RNTester gains a Blob example that builds a blob per BlobPart variant, reads each back through readAsArrayBuffer, and compares the bytes.
• Android and C++ API snapshots updated.

[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