Delegation and overrides:

- Tests.
- No need for a separate diagnostic message regarding
return/property type conflict on override by delegation:
it is always a conflict of inherited signatures.

compiler/testData/diagnostics/tests/delegation/clashes/varOverriddenByVal.kt

@@ -0,0 +1,29 @@
+interface IVar {
+    var foo: Int
+}
+
+interface IDerived : IVar
+
+interface IVal {
+    val foo: Int
+}
+
+class CVal : IVal {
+    override val foo: Int get() = 42
+}
+
+interface IValT<T> {
+    val foo: T
+}
+
+class CValT<T> : IValT<T> {
+    override val foo: T get() = null!!
+}
+
+abstract <!VAR_OVERRIDDEN_BY_VAL_BY_DELEGATION!>class Test1<!> : IVar, IVal by CVal()
+
+abstract <!VAR_OVERRIDDEN_BY_VAL_BY_DELEGATION!>class Test2<!> : IVar, IValT<Int> by CValT<Int>()
+
+abstract <!VAR_OVERRIDDEN_BY_VAL_BY_DELEGATION!>class Test3<!> : IDerived, IVal by CVal()
+
+abstract <!VAR_OVERRIDDEN_BY_VAL_BY_DELEGATION!>class Test4<!> : IDerived, IValT<Int> by CValT<Int>()