Compile type_annotations as Java 8

Rollback of f1308a0 + ecfc4fc, see discussion in unknown commit

JDK 17+ is required for running the Error Prone static analysis tool as part of builds, but this keeps library jars that are used by projects that don't build with Error Prone as compatible as possible.

PiperOrigin-RevId: 700118371

type_annotations/pom.xml

@@ -43,4 +43,18 @@
       <url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
     </license>
   </licenses>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <configuration>
+          <source>8</source>
+          <target>8</target>
+          <compilerArgs combine.self="override" />
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
 </project>