Introduce tests runner for run configurations + highlighting + Gradle

This allows us to check two things:
- presence of line markers (haven't been checked by old
  GradleTestRunConfigurationTests, though could've been checked by
  LineMarkerTests)
- some properties of run configurations which will be created from those
  line markers

Old GradleTestRunConfigurationTest have been renamed to
GradleTestRunConfigurationCustomTest and slightly modified to be able
to re-use the same testdata if necessary.

idea/testData/gradle/testRunConfigurations/preferredConfigurations/src/test/kotlin/MyKotlinTest.kt

@@ -1,11 +1,11 @@
 import org.junit.Test
 
-class MyKotlinTest {
+class <lineMarker descr="Run Test" settings=":cleanTest :test --tests \"MyKotlinTest\"">MyKotlinTest</lineMarker> {
     @Test
-    fun testA() {
+    fun <lineMarker descr="Run Test" settings=":cleanTest :test --tests \"MyKotlinTest.testA\"">testA</lineMarker>() {
     }
 
     @Test
-    fun testB() {
+    fun <lineMarker descr="Run Test" settings=":cleanTest :test --tests \"MyKotlinTest.testB\"">testB</lineMarker>() {
     }
 }