refactor Spotlight to use native android and cocoa Spotlight integrations when using Flutter

[buenaflor]

Description

Currently the Spotlight transport is implemented on the Dart layer and is a decorator for the existing transport but it does not show the final envelope that is actually being sent because on Android for example the envelope is still being processed after captureEnvelope is called

So this is the goal:

• Android uses the Android spotlight integration
• Cocoa uses the Cocoa spotlight integration
• Web keeps using SpotlightHttpTransport because we don't have a JS SDK integration yet but this may change soon
• Linux, Windows will also keep using SpotlightHttpTransport