KT-4960 Redeclaration is not reported for type parameters of interfaces

When resolving a class body for a class without a primary constructor
(e.g., an interface), no checks were performed for redeclarations
in the corresponding class header.
Creating & initializing a lexical scope of an appropriate kind will do it.
Note that since class has no primary constructor, only type parameters
could be redeclared (and that's KT-4960).

compiler/testData/diagnostics/tests/redeclarations/interfaceTypeParameters.kt

@@ -0,0 +1,6 @@
+interface Test1<<!REDECLARATION!>T<!>, <!REDECLARATION!>T<!>>
+interface Test2<<!REDECLARATION!>X<!>, Y, <!REDECLARATION!>X<!>>
+
+class Outer<T> {
+    interface TestNested<T>
+}

compiler/testData/diagnostics/tests/redeclarations/interfaceTypeParameters.txt

@@ -0,0 +1,26 @@
+package
+
+public final class Outer</*0*/ T> {
+    public constructor Outer</*0*/ T>()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    public interface TestNested</*0*/ T> {
+        public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+        public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+        public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    }
+}
+
+public interface Test1</*0*/ T, /*1*/ T> {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface Test2</*0*/ X, /*1*/ Y, /*2*/ X> {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}