Extract 'test-generator' module out of 'generators'

Also avoid using intellij API where kotlin-stdlib can be used instead

gradle/project-schema.json

@@ -2769,7 +2769,8 @@
             "testImplementation",
             "testRuntime",
             "testRuntimeClasspath",
-            "testRuntimeOnly"
+            "testRuntimeOnly",
+            "tests-jar"
         ],
         "extensions": {
             "ext": "org.gradle.api.plugins.ExtraPropertiesExtension",
@@ -2804,7 +2805,8 @@
             "testImplementation",
             "testRuntime",
             "testRuntimeClasspath",
-            "testRuntimeOnly"
+            "testRuntimeOnly",
+            "tests-jar"
         ],
         "extensions": {
             "ext": "org.gradle.api.plugins.ExtraPropertiesExtension",
@@ -3052,6 +3054,41 @@
             "reporting": "org.gradle.api.reporting.ReportingExtension"
         }
     },
+    ":generators:test-generator": {
+        "conventions": {
+            "base": "org.gradle.api.plugins.BasePluginConvention",
+            "java": "org.gradle.api.plugins.JavaPluginConvention"
+        },
+        "configurations": [
+            "apiElements",
+            "archives",
+            "compile",
+            "compileClasspath",
+            "compileOnly",
+            "default",
+            "implementation",
+            "kapt",
+            "kaptTest",
+            "runtime",
+            "runtimeClasspath",
+            "runtimeElements",
+            "runtimeOnly",
+            "testCompile",
+            "testCompileClasspath",
+            "testCompileOnly",
+            "testImplementation",
+            "testRuntime",
+            "testRuntimeClasspath",
+            "testRuntimeOnly"
+        ],
+        "extensions": {
+            "ext": "org.gradle.api.plugins.ExtraPropertiesExtension",
+            "kotlin": "org.jetbrains.kotlin.gradle.dsl.KotlinJvmProjectExtension",
+            "kapt": "org.jetbrains.kotlin.gradle.plugin.KaptExtension",
+            "defaultArtifacts": "org.gradle.api.internal.plugins.DefaultArtifactPublicationSet",
+            "reporting": "org.gradle.api.reporting.ReportingExtension"
+        }
+    },
     ":idea:formatter": {
         "conventions": {
             "base": "org.gradle.api.plugins.BasePluginConvention",