make smart completion work in java extends/implements clauses (IDEA-38166)

java/java-tests/testData/codeInsight/completion/smartType/OnlyInterfacesInImplements-out.java

@@ -0,0 +1,7 @@
+public class Main implements XFooIntf<caret> {
+
+}
+
+class XFoo1 {}
+class XFoo2 {}
+interface XFooIntf {}

java/java-tests/testData/codeInsight/completion/smartType/OnlyInterfacesInImplements.java

@@ -0,0 +1,7 @@
+public class Main implements XF<caret> {
+
+}
+
+class XFoo1 {}
+class XFoo2 {}
+interface XFooIntf {}