Revert to AGP 8.7.3

[nbradbury]

As a companion to this WPAndroid PR, this PR reverts AGP to v8.7.3. Please refer to that WPAndroid PR for details.

[Copilot]

Pull Request Overview

This PR reverts the Android Gradle Plugin version to 8.7.3 to align with a companion WPAndroid PR.

• Reverting AGP from 8.8.1 to 8.7.3
• Maintaining compatibility with the referenced WPAndroid changes

[dcalhoun]

I tested running the following and all functioned as expected:

• The GBK Demo app.
• WP-Android with a GBK composite build.
• WP-Android with a GBK binary depedency.
• ./gradlew assembleRelease.
• ./gradlew lintRelease

I note that the previous Gradle upgrade included additional file changes:

• android/gradle/wrapper/gradle-wrapper.jar
• android/gradle/wrapper/gradle-wrapper.properties
• android/gradlew
• android/gradlew.bat

I presume we do not need to make similar changes, but @ParaskP7 will you confirm?

[ParaskP7]

I presume we do not need to make similar changes, but @ParaskP7 will you confirm?

You're right @nbradbury , no need to do any Gradle up/downgrade with this change, downgrading and thus touching AGP only should be all we need from this.