Resolve android_build_all_packages Warnings (#9643)

Addressed versioning warnings by updating the following dependencies to their minimum supported versions:

Gradle: 8.7
AGP: 8.6.0
KGP: 2.1.0

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Author: jesswrd

.ci/legacy_project/README.md

@@ -41,13 +41,16 @@ and then deleting everything but `android/` from it:
   `build.gradle` to maintain compatibility with plugins that use
   Flutter's most recently supported API version.
 - Modifies `gradle-wrapper.properties` to upgrade the Gradle version
-  from 6.7 to 8.4. If a user runs into an error with the Gradle
+  from 8.4 to 8.7. If a user runs into an error with the Gradle
   version, the warning is clear on how to upgrade the version to
   one that we support.
 - Modifies `settings.gradle` to upgrade the Android Gradle Plugin (AGP)
-  from version 4.1.0 (originally set in `build.gradle`; see bullet below)
-  to 8.3.0. If a user runs into an error with the AGP version, the warning
+  from version 8.3.0 (originally set in `build.gradle`; see bullet below)
+  to 8.6.0. If a user runs into an error with the AGP version, the warning
   is clear on how to upgrade the version to one that we support.
 - Refactor plugin to use declarative Gradle apply instead of the
   imperative apply (this includes moving where the Android Gradle
   Plugin (AGP) version is set from `build.gradle` to `settings.gradle`).
+- Modifies `settings.gradle` to upgrade the Kotlin Gradle Plugin (KGP)
+  from version 1.9.0 to 2.1.0. If a user runs into an error with the AGP version,
+  the warning is clear on how to upgrade the version to one that we support.

.ci/legacy_project/all_packages/android/gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.4-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.7-all.zip

.ci/legacy_project/all_packages/android/settings.gradle

@@ -19,8 +19,8 @@ pluginManagement {
 // See https://github.com/flutter/flutter/blob/master/docs/ecosystem/Plugins-and-Packages-repository-structure.md#gradle-structure for more info.
 plugins {
     id "dev.flutter.flutter-plugin-loader" version "1.0.0"
-    id "com.android.application" version "8.3.0" apply false
-    id "org.jetbrains.kotlin.android" version "1.9.0" apply false
+    id "com.android.application" version "8.6.0" apply false
+    id "org.jetbrains.kotlin.android" version "2.1.0" apply false
 }
 
 include ":app"