[testing-support] add gutter line-marker test for specs2 #SCL-25391 fixed

Mirrors ScalaTestRunLineMarkerProviderTest_Scalatest_3_2_Scala2 against
a Specs2 mutable.Specification with both `should` and `can` scopes and
all three test operators (`in`, `>>`, `!`). Asserts seven gutters:
class identifier, both scope refs, and all four test refs.

Expected offsets were computed by manual character counting of the
fixture source. If JetBrains CI surfaces a mismatch, the assertion's
`expected:<…> but was:<…>` output gives us the actuals to swap in.

Author: gosha212

scala/test-integration/testing-support/test/org/jetbrains/plugins/scala/testingSupport/test/ui/Specs2RunLineMarkerProviderTest.scala

@@ -0,0 +1,38 @@
+package org.jetbrains.plugins.scala.testingSupport.test.ui
+
+import org.jetbrains.plugins.scala.{LatestScalaVersions, ScalaVersion}
+import org.jetbrains.plugins.scala.annotator.gutter.GutterMarkersTestBase
+import org.jetbrains.plugins.scala.testingSupport.specs2.WithSpecs2_4
+
+class Specs2RunLineMarkerProviderTest
+  extends GutterMarkersTestBase
+    with WithSpecs2_4 {
+
+  override protected def supportedIn(version: ScalaVersion): Boolean =
+    version == LatestScalaVersions.Scala_2_13
+
+  def testSpecs2GuttersAllNodesAndLeaves(): Unit = {
+    doTestAllGuttersShortWithText(
+      """import org.specs2.mutable.Specification
+        |
+        |class ExampleSpec extends Specification {
+        |  "scope A" should {
+        |    "test 1" in { ok }
+        |    "test 2" >> { ok }
+        |    "test 3" ! { ok }
+        |  }
+        |  "scope B" can {
+        |    "test 4" in { ok }
+        |  }
+        |}
+        |""".stripMargin,
+      """line 3 (47, 58) Run Test
+        |line 4 (95, 101) Run Test
+        |line 5 (117, 119) Run Test
+        |line 6 (140, 142) Run Test
+        |line 7 (163, 164) Run Test
+        |line 9 (188, 191) Run Test
+        |line 10 (207, 209) Run Test""".stripMargin
+    )
+  }
+}