Use JDK 21 for Eclipse plugin

The plugin is failing to build after changes in [1] to add usages of records.

[1] 4962993

https://github.com/google/google-java-format/actions/runs/22568168992/job/65368984173

PiperOrigin-RevId: 877811635

Author: cushon

eclipse_plugin/META-INF/MANIFEST.MF

@@ -4,7 +4,7 @@ Bundle-Name: google-java-format
 Bundle-SymbolicName: google-java-format-eclipse-plugin;singleton:=true
 Bundle-Vendor: Google
 Bundle-Version: 1.31.0
-Bundle-RequiredExecutionEnvironment: JavaSE-11
+Bundle-RequiredExecutionEnvironment: JavaSE-21
 Require-Bundle: org.eclipse.jdt.core;bundle-version="3.10.0",
  org.eclipse.jface,
  org.eclipse.text,

eclipse_plugin/pom.xml

@@ -32,7 +32,7 @@
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-    <tycho-version>3.0.5</tycho-version>
+    <tycho-version>5.0.2</tycho-version>
   </properties>
 
   <dependencies>
@@ -132,8 +132,8 @@
         <artifactId>maven-compiler-plugin</artifactId>
         <version>3.7.0</version>
         <configuration>
-          <source>11</source>
-          <target>11</target>
+          <source>21</source>
+          <target>21</target>
         </configuration>
       </plugin>
     </plugins>