Fix TestServer to include transitive dependencies

Test workspaces should be created with the complete dependency classpath
of their dependencies. The classpath was wrongly built with only the
class directory of their dependencies.

Author: Duhemm

language-server/test/dotty/tools/languageserver/DefinitionTest.scala

@@ -28,9 +28,14 @@ class DefinitionTest {
       code"""class Bar { new ${m3}Foo${m4} }"""
     )
 
-    withWorkspaces(w0, w1)
+    val w2 = Workspace.dependingOn(w1).withSources(
+      code"""class Baz extends ${m5}Foo${m6}"""
+    )
+
+    withWorkspaces(w0, w1, w2)
       .definition(m1 to m2, List(m1 to m2))
       .definition(m3 to m4, List(m1 to m2))
+      .definition(m5 to m6, List(m1 to m2))
   }
 
   @Test def valDefinition0: Unit = {

language-server/test/dotty/tools/languageserver/util/server/TestServer.scala

@@ -100,9 +100,12 @@ class TestServer(testFolder: Path, workspaces: List[Workspace]) {
     path.toAbsolutePath
   }
 
-  private def dependencyClasspath(workspace: Workspace) =
+  private def dependencyClasspath(workspace: Workspace): Seq[String] = {
     BuildInfo.ideTestsDependencyClasspath.map(_.getAbsolutePath) ++
-      workspace.dependsOn.map(w => classDirectory(w, wipe = false).toString)
+      workspace.dependsOn.flatMap { dep =>
+        classDirectory(dep, wipe = false).toString +: dependencyClasspath(dep)
+      }
+  }.distinct
 
   private def sourceDirectory(workspace: Workspace, wipe: Boolean): Path = {
     val path = TestFile.sourceDir.resolve(workspace.name).toAbsolutePath