GrapheneOS Messages 13 hardens MMS parsers and Android IPC hygiene

Version 13 of the GrapheneOS Messages app adds allocation limits to its EXIF APP1, MMS PDU, and MMS content-type parsers, fixes GIF null dereferences, and adds a dimension check before native transcoding. It also unexports widget receivers, uses FLAG_IMMUTABLE for pending intents, and validates shared content. The build targets minSdk 36, targetSdk 37, and compileSdk 37.

• Allocation caps added to EXIF APP1, MMS PDU, and content-type parsers
• Widget receivers unexported and FLAG_IMMUTABLE applied to pending intents
• Dimension validation before native transcoding and GIF null check fixed
• Requires minSdk 36, targetSdk 37, compileSdk 37