Drop Protobuf support for Android KitKat per EOL and add existing minimum Java 1.8 in Maven pom.xmls

See https://android-developers.googleblog.com/2023/07/google-play-services-discontinuing-updates-for-kitkat.html for more details on Android KitKat EOL.

PiperOrigin-RevId: 600609333

java/pom.xml

@@ -178,10 +178,15 @@
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>animal-sniffer-maven-plugin</artifactId>
         <configuration>
+          <signature>
+            <groupId>org.codehaus.mojo.signature</groupId>
+            <artifactId>java18</artifactId>
+            <version>1.0</version>
+          </signature>
           <signature>
             <groupId>net.sf.androidscents.signature</groupId>
-            <artifactId>android-api-level-14</artifactId>
-            <version>4.0_r4</version>
+            <artifactId>android-api-level-21</artifactId>
+            <version>5.0.1_r2</version>
           </signature>
           <ignores>
             <ignore>sun.misc.Unsafe</ignore>

java/util/pom.xml

@@ -122,10 +122,15 @@
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>animal-sniffer-maven-plugin</artifactId>
         <configuration>
+          <signature>
+            <groupId>org.codehaus.mojo.signature</groupId>
+            <artifactId>java18</artifactId>
+            <version>1.0</version>
+          </signature>
           <signature>
             <groupId>net.sf.androidscents.signature</groupId>
-            <artifactId>android-api-level-19</artifactId>
-            <version>4.4.2_r4</version>
+            <artifactId>android-api-level-21</artifactId>
+            <version>5.0.1_r2</version>
           </signature>
         </configuration>
         <executions>