feat: support source-map debug images on JS exceptions

[dcalhoun]

What

Adds an optional way for JSExceptions to carry source-map debug images, so
JavaScript exceptions can be symbolicated in Sentry via Debug IDs rather than
by file path.

• New JSDebugImage protocol (codeFile, debugID).
• New optional JSException.debugImages: [JSDebugImage] property, defaulted to
  [] via a protocol extension.
• When a JSException provides debug images, SentryEventJSException attaches
  them as type: "sourcemap" entries on the event's debug_meta. serialize()
  now preserves debug_meta only when such images are present.

Why

Consumers whose JavaScript runs from unstable on-device paths — e.g.
GutenbergKit, which loads editor JS in a WKWebView from a per-install bundle
directory (file:///var/containers/Bundle/Application/<random-UUID>/…/assets/index-*.js) —
cannot be symbolicated by Sentry's path-based source-map matching: the artifact
name can never equal a path containing a per-install random UUID.

Debug IDs solve this by matching a minified file to its source map via an
injected ID, independent of path or release. For that to work, the event must
carry the debug image, but SentryEventJSException.serialize() previously
stripped debug_meta unconditionally. This change lets a consumer supply the
debug images and have them reach Sentry.

Backward compatibility

debugImages is optional with a [] default, so existing conformers (the React
Native / gutenberg-mobile path) require no changes and behave identically:
they supply no images, the array is empty, and debug_meta stays stripped
exactly as before.

Testing

New SentryEventJSExceptionTests (all passing):

• With debug images → serialize() emits debug_meta.images with
  type: "sourcemap", code_file, debug_id.

• Without debug images → debug_meta is absent (matches prior behavior).

• A conformer that doesn't implement debugImages gets the [] default.

• I have considered if this change warrants release notes and have added them to the appropriate section in the CHANGELOG.md if necessary.