[floydkim]

Purpose

Allow apps to record CodePush download file sizes by version without tracking download progress themselves.

onDownloadSuccess(targetVersion, { baseVersion, downloadBytes }) now provides the version running before the update and the size of the final downloaded file used for the update. When running the embedded bundle, the base version is the native app version.

• A successful patch reports the patch file size. A fallback to a full download reports only the final full file size, excluding earlier failed attempts.
• Measurement works without a progress callback. Existing callbacks that accept only the target version remain compatible.
• Download size reporting requires rebuilding the native app. Older native code returns null for downloadBytes.
• Apps that call remotePackage.download() directly can read the same size from localPackage.downloadBytes. It is not saved with the update, so getCurrentPackage() and getUpdateMetadata() do not return it.

Validation

• Passed 83 JavaScript tests and source type checking against the latest master at the time of the update.
• Passed Android native tests against that master, including comparisons with actual file sizes for full downloads, patches, fallbacks, and responses without Content-Length. These cover the sizes the update manager reports, not the native module's callback wiring, because the module cannot be constructed in JVM tests. The iOS tests cover that wiring by calling the module entry point.
• Passed 67 iOS native tests before moving the changes onto the latest master, including comparisons between native method return values and actual file sizes.
• Confirmed that deliberately incorrect measurements cause the five new Android tests and three new iOS tests to fail.
• App E2E tests and actual telemetry delivery were not exercised.

The implementation and JavaScript tests, native test coverage, and documentation are split into separate commits.