Clean: upgrade deprecated code in Plugins
- Replacing WWW with UnityWebRequest, also updated success checks to more generic versions
- Texture.Resize -> Texture.Reinitialize
- Mute deprecation warning when accessing a value (since we validate beforehand)
- EditorGUILayout.EnumMaskField -> EditorGUILayout.EnumFlagsField
Tests: Booted up local session - no new warnings/errors in logs, code took expected branches