fix: Use testFixture notation, instead of project's compile test fixture task output

Especially, the test fixtures of the servlet instrumentation needs to
export their dependencies to :dd-java-agent:testing

Author: bric3

dd-java-agent/instrumentation/liberty-20/build.gradle

@@ -37,8 +37,7 @@ dependencies {
   webappCompileOnly group: 'javax.servlet', name: 'javax.servlet-api', version: '3.1.0'
   // compileOnly to avoid bringing all the test dependencies to the test app
   // these are to be provided by the system classloader on test time
-  webappCompileOnly project(':dd-java-agent:instrumentation:servlet:request-3')
-    .tasks['compileTestFixturesJava'].classpath
+  webappCompileOnly testFixtures(project(':dd-java-agent:instrumentation:servlet:request-3'))
   // only the testFixtures jar (not its dependencies) and groovy should be included in the webapp
   webappImplementation files(
     project(':dd-java-agent:instrumentation:servlet:request-3')

dd-java-agent/instrumentation/liberty-23/build.gradle

@@ -41,8 +41,7 @@ dependencies {
   webappCompileOnly group: 'jakarta.servlet', name: 'jakarta.servlet-api', version: '5.0.0'
   // compileOnly to avoid bringing all the test dependencies to the test app
   // these are to be provided by the system classloader on test time
-  webappCompileOnly project(':dd-java-agent:instrumentation:servlet:request-5')
-    .tasks['compileTestFixturesJava'].classpath
+  webappCompileOnly testFixtures(project(':dd-java-agent:instrumentation:servlet:request-5'))
   // only the testFixtures jar (not its dependencies) and groovy should be included in the webapp
   webappImplementation files(
     project(':dd-java-agent:instrumentation:servlet:request-5')

dd-java-agent/instrumentation/servlet/request-3/build.gradle

@@ -38,7 +38,7 @@ dependencies {
   compileOnly group: 'javax.servlet', name: 'javax.servlet-api', version: '3.1.0'
   implementation project(':dd-java-agent:instrumentation:servlet-common')
 
-  testFixturesImplementation(project(':dd-java-agent:testing')) {
+  testFixturesApi(project(':dd-java-agent:testing')) {
     exclude group: 'org.eclipse.jetty', module: 'jetty-server'
   }
   testFixturesCompileOnly group: 'javax.servlet', name: 'javax.servlet-api', version: '3.0.1'

dd-java-agent/instrumentation/servlet/request-5/build.gradle

@@ -64,7 +64,7 @@ dependencies {
     transitive = false
   }
 
-  testFixturesImplementation(project(':dd-java-agent:testing')) {
+  testFixturesApi(project(':dd-java-agent:testing')) {
     exclude group: 'org.eclipse.jetty', module: 'jetty-server'
   }
   testFixturesCompileOnly group: 'jakarta.servlet', name: 'jakarta.servlet-api', version: '5.0.0'