Test Clipboard image operations and unify the behavior on all platforms

[EchoEllet]

• If the user copies an image that's not a GIF and the platform they're using supports GIF (Android and iOS only), then we might not return a GIF image in case of calling getClipboardImage() (see related todo), or instead (what might probably do), will return the GIF image as standard image in case of getClipboardImage regardless if it's GIF, and document this in getClipboardGif and getClipboardImage that should check for getClipboardGif first and then getClipboardImage if expect Gif image that's animated. If this is the new expected behavior then update the related code on Android, remove the TODO above (The TODO is outdated and suggested a different behavior), document the change in quill_native_bridge and test the behavior manually on all platforms to ensure consistency.
• Test copyImageToClipboard() and getClipboardImage() on all platforms with different and common image types. Ensure consistency and unified behavior when possible.

Part of singerdmx/flutter-quill#2230