jgvariant-tool: Add Maven exec plugin for direct execution.

Change-Id: I683100e55a9ba06028bc0d92af4087c5749ad4ad
diff --git a/jgvariant-parent/pom.xml b/jgvariant-parent/pom.xml
index 4d053fc..0fadc4c 100644
--- a/jgvariant-parent/pom.xml
+++ b/jgvariant-parent/pom.xml
@@ -56,6 +56,7 @@
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
 
     <compiler-plugin.version>3.11.0</compiler-plugin.version>
+    <exec-plugin.version>3.1.0</exec-plugin.version>
     <failsafe-plugin.version>${surefire-plugin.version}</failsafe-plugin.version>
     <flatten-plugin.version>1.5.0</flatten-plugin.version>
     <jar-plugin.version>3.3.0</jar-plugin.version>
@@ -266,6 +267,12 @@
         </plugin>
 
         <plugin>
+          <groupId>org.codehaus.mojo</groupId>
+          <artifactId>exec-maven-plugin</artifactId>
+          <version>${exec-plugin.version}</version>
+        </plugin>
+
+        <plugin>
           <groupId>org.graalvm.buildtools</groupId>
           <artifactId>native-maven-plugin</artifactId>
           <version>${native-plugin.version}</version>