chore(android_intent_plus): modernize Android build config according to Gradle 8

[mdmahendri]

Description

This PR is part of #3867 aimed at removing warnings related to Gradle and unused configurations. The goal is to minimize technical debt ahead of the migration to AGP 9.

Tested locally with Flutter 3.38.1. The only remaining warnings are due to Flutter 3.38.1 using a library version higher than the hardcoded version in the plugin.

In addition to the changes described in the linked PR, this includes:

• removing package attribute from manifests for the warning

  Setting the namespace via a source AndroidManifest.xml's package attribute is deprecated.
  

  This fix aligns with the Official Android Developer Documentation:

  In the Gradle-based build system, starting with AGP 7.3, don't set the package value in the source manifest file directly.

Related Issues

• Partially fixes [Request]: Clean up deprecated build features and warnings in Gradle 8 #3864

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• No, this is not a breaking change.