Replace Gradle conventions with configuration blocks. (#341)

Access to plugin conventions has been deprecated and is scheduled to be removed in Gradle 9.0.

See: https://docs.gradle.org/8.6/userguide/upgrading_version_8.html#deprecated_access_to_conventions

gradle/source-layout.gradle

@@ -22,5 +22,7 @@ jar {
 }
 
 plugins.withId('war') {
-  webAppDirName = 'src/main/webapp'
+  war {
+    webAppDirectory = file('src/main/webapp')
+  }
 }

metafix-ide/build.gradle

@@ -12,11 +12,13 @@ dependencies {
 apply plugin: 'application'
 apply plugin: 'com.github.johnrengelman.shadow'
 
-mainClassName = 'org.eclipse.xtext.ide.server.ServerLauncher'
-applicationName = 'xtext-server'
+application {
+  mainClass = 'org.eclipse.xtext.ide.server.ServerLauncher'
+  applicationName = 'xtext-server'
+}
 
 shadowJar {
-  from(project.convention.getPlugin(JavaPluginConvention).sourceSets.main.output)
+  from(sourceSets.main.output)
   configurations = [project.configurations.runtimeClasspath]
 
   exclude(