ci: Upgrade to JDK 21 and centralize CI configuration with new workflows (#4948)

.github/actions/gradle-setup/action.yml

@@ -0,0 +1,35 @@
+name: Gradle Setup
+description: Setup Java and Gradle for KMP builds
+inputs:
+  cache_read_only:
+    description: 'Whether Gradle cache is read-only'
+    default: 'true'
+  jdk_distribution:
+    description: 'JDK distribution (temurin or jetbrains)'
+    default: 'temurin'
+  gradle_encryption_key:
+    description: 'Encryption key for Gradle remote cache'
+    required: false
+runs:
+  using: composite
+  steps:
+    - name: Validate Gradle Wrapper
+      uses: gradle/actions/wrapper-validation@v6
+
+    - name: Set up JDK 21
+      uses: actions/setup-java@v5
+      with:
+        java-version: '21'
+        distribution: ${{ inputs.jdk_distribution }}
+        token: ${{ github.token }}
+
+    - name: Setup Gradle
+      uses: gradle/actions/setup-gradle@v6
+      with:
+        cache-read-only: ${{ inputs.cache_read_only }}
+        cache-encryption-key: ${{ inputs.gradle_encryption_key }}
+        cache-cleanup: on-success
+        build-scan-publish: true
+        build-scan-terms-of-use-url: 'https://gradle.com/terms-of-service'
+        build-scan-terms-of-use-agree: 'yes'
+        add-job-summary: always