[Build] Add jUnit dependencies in testApiJUnit5 to the implementation configuration

Adding these dependencies to the `api` configuration pollutes classpath for each dependant modules even if it doesn't need them. Instead, the dependencies should be declared more granularly if they're required
#KTI-1349 In Progress

generators/test-generator/build.gradle.kts

@@ -8,7 +8,7 @@ dependencies {
     testApi(project(":core:util.runtime"))
     testApi(projectTests(":compiler:test-infrastructure-utils"))
     testApi(kotlinStdlib())
-    testApi(libs.junit4)
+    testImplementation(libs.junit4)
     testApiJUnit5()
     testApi(project(":generators"))