Upgrade build dependencies for the project

- Upgrade to Gradle 8.11
- Upgrade to Android Gradle Plugin 8.7.2
- Remove deprecated android.defaults.buildfeatures.buildconfig=true
  gradle property, it is not needed as mastodon/build.gradle already
  sets android { buildFeatures { buildConfig true } }
- Move plugin repository definition to settings.gradle to match latest
  Gradle practices
- Move to using plugin {} mechanism to add Android Gradle Plugin to
  match the latest Gradle practices
- Remove root project clean task as this project does not produce any
  real artifacts, it seems to be leftover from original Android new
  project template

build.gradle

@@ -1,23 +1,3 @@
-// Top-level build file where you can add configuration options common to all sub-projects/modules.
-buildscript {
-	repositories {
-		google()
-		mavenCentral()
-		maven {
-			url "https://www.jitpack.io"
-			content {
-				includeModule 'com.github.UnifiedPush', 'android-connector'
-			}
-		}
-		mavenLocal()
-	}
-	dependencies {
-		classpath 'com.android.tools.build:gradle:8.0.0'
-		// NOTE: Do not place your application dependencies here; they belong
-		// in the individual module build.gradle files
-	}
+plugins {
+	id("com.android.application") version("8.7.2") apply(false)
 }
-
-task clean(type: Delete) {
-	delete rootProject.buildDir
-}