Fix pts with testng (#5339)

Motivation:

Recently we have enabled PTS which causes an error when trying to run testNg tests.
```
Execution failed for task ':core:testNg'.
> Predictive Test Selection only supports JUnit Platform.
```

It has been pointed out that `TestNg` is supported through `junit-platform`.
ref: https://docs.gradle.com/enterprise/predictive-test-selection/#_frameworks_and_languages

I see no reason we shouldn't just use `junit-platform` overall as our default test framework launcher.

ref: https://gradle.slack.com/archives/C05975D6V7H/p1701969512592219

Note that we are unable to add the testNg globally by default due to the following issue: junit-team/testng-engine#87

Modifications:

- Added a test engine `testng` to testing runtime
- Modified to always use `useJUnitPlatform()`

Result:

- We can run testNg tests with PTS enabled

build.gradle

@@ -70,6 +70,8 @@ allprojects {
     tasks.withType(Test) {
         jvmArgumentProviders.add(new TestBuildDirArgumentsProvider(project.buildDir))
 
+        useJUnitPlatform()
+
         // Do not omit stack frames for easier tracking.
         jvmArgs '-XX:-OmitStackTraceInFastThrow'
 

core/build.gradle

@@ -35,7 +35,6 @@ mrJarVersions.each { version->
         testClassesDirs = sourceSets."java${version}Test".output.classesDirs
         classpath = sourceSets."java${version}Test".runtimeClasspath
 
-        useJUnitPlatform()
         project.ext.configureCommonTestSettings(it)
         enabled = project.ext.testJavaVersion >= targetJavaVersion
     }
@@ -225,6 +224,9 @@ if (rootProject.findProperty('flakyTests') != 'true') {
                     }
                 }
             }
+            dependencies {
+                runtimeOnly libs.junit.testng.engine
+            }
         }
     }
     tasks.shadedTest.finalizedBy testing.suites.testNg

dependencies.toml

@@ -724,6 +724,10 @@ module = "org.junit.platform:junit-platform-launcher"
 module = "org.junit-pioneer:junit-pioneer"
 version.ref = "junit-pioneer"
 
+[libraries.junit-testng-engine]
+module = "org.junit.support:testng-engine"
+version = "1.0.4"
+
 [libraries.jwt]
 module = "com.auth0:java-jwt"
 version.ref = "jwt"

kotlin/build.gradle.kts

@@ -31,6 +31,10 @@ testing {
                     }
                 }
             }
+
+            dependencies {
+                runtimeOnly(libs.junit.testng.engine)
+            }
         }
     }
 }