Replace packagingOptions to packaging if AGP is 8.0+

[argzdev]

Fixes #715.

Due to incompatibility of the packagingOptions keyword in Unity 6, this will create unecessary mainTemplate.gradle.backup. Android keyword Packaging is introduced in Android Gradle Plugin version 8.0+.

Use packaging keyword if AGP version is 8.0+, else use packagingOptions

Unity version	Gradle version	Android Gradle Plug-in version
Unity-6	8.4	8.3.0
2022.3	7.5.1	7.4.2
2021.3	7.5.1	7.4.2

e.g.

// Android Resolver Exclusions Start
android {
  packaging {
      exclude ('/lib/arm64-v8a/*' + '*')
      exclude ('/lib/armeabi/*' + '*')
      exclude ('/lib/mips/*' + '*')
      exclude ('/lib/mips64/*' + '*')
      exclude ('/lib/x86/*' + '*')
      exclude ('/lib/x86_64/*' + '*')
  }