Bump to Gradle 8.10.2, require Java 11

Bump Gradle from 6.8.3 to 8.10.2 and increase the minimum required
Java version from 8 to 11 (SMACK-953).

The switch from Java 8 to 11 caused some Bytecode portability issues
regarding NIO Buffers. Java changed with version 9 the return type of
some subclasses of Buffer to return the specific Buffer type instead
of the Buffer superclass [JDK-4774077]. For example, ByteBuffer.filp()
previously returned Buffer, while it does return ByteBuffer now.

This sensible change was not reflected by the Android API [1], which
means that AnimalSniffer rightfully started to complain that there is
no method "ByteBuffer ByteBuffer.flip()" in Android, there is only
"Buffer ByteBuffer.flip()", and those are incompatible methods on
Java's Bytecode layer.

As workaround, this changes

    return charBuffer.flip().toString();

to

    ((java.nio.Buffer) charBuffer).flip();
    return charBuffer.toString();

to restore the Bytecode portability between Android and Java.

Errorprone also got new checks, of which JavaUtilDate and JdkObsolete
are wroth mentioning.

JavaUtilData basically strongly recommends to use Java's newer time
API over java.util.Date. But since Smack was Java 8 until now,
j.u.Date is widely used.

Similar JdkObsolete mentions obsolete JDK APIs, like data structures
like Vector and Stack. But mostly LinkedList, which should usually be
replaced by ArrayList. And this is what this commit largely does.

JDK-4774077: https://bugs.openjdk.org/browse/JDK-4774077
1: https://issuetracker.google.com/issues/369219141

.github/workflows/ci.yml

@@ -6,13 +6,13 @@ jobs:
   build:
     name: Build Smack
 
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         java:
-          - 11
+          - 17
     env:
-      PRIMARY_JAVA_VERSION: 11
+      PRIMARY_JAVA_VERSION: 17
 
     steps:
       - name: Checkout
@@ -57,6 +57,17 @@ jobs:
         run: |
           sdkmanager "platforms;android-21"
 
+      # Workaround
+      - name: Create gradle.properties
+        run: |
+          cat <<-EOF > gradle.properties
+          # Workaround for https://github.com/CycloneDX/cyclonedx-gradle-plugin/issues/349
+          # suggested at https://docs.gradle.org/current/userguide/upgrading_version_8.html#xml_parsing_now_requires_recent_parsers
+          systemProp.javax.xml.parsers.SAXParserFactory=com.sun.org.apache.xerces.internal.jaxp.SAXParserFactoryImpl
+          systemProp.javax.xml.transform.TransformerFactory=com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl
+          systemProp.javax.xml.parsers.DocumentBuilderFactory=com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl
+          EOF
+
       # Testing
       - name: Gradle Check
         run: ./gradlew check --stacktrace
@@ -72,10 +83,19 @@ jobs:
 
       # Test Coverage Report
       - name: Jacoco Test Coverage
-        if: ${{ matrix.java == env.PRIMARY_JAVA_VERSION }}
-        run: ./gradlew jacocoRootReport coveralls
         env:
-          COVERALLS_REPO_TOKEN: S2ecSJja2cKJa9yv45C8ZFPohXuRrTXKd
+          COVERALLS_REPO_TOKEN: ${{ secrets.COVERALLS_REPO_TOKEN }}
+        if: |
+          ${{ matrix.java == env.PRIMARY_JAVA_VERSION }} &&
+          ${{ env.COVERALLS_REPO_TOKEN != '' }}
+        run: |
+          if [[ -z ${COVERALLS_REPO_TOKEN} ]]; then
+              echo WARNING: COVERALLS_REPO_TOKEN is empty
+          else
+              echo COVERALLS_REPO_TOKEN is not empty
+          fi
+          ./gradlew smack-java8-full:testCodeCoverageReport
+          ./gradlew smack-java8-full:coveralls
 
       # Upload build artifacts
       - name: Upload build artifacts