FIR: introduce FunInterfaceDeclarationChecker

compiler/testData/diagnostics/tests/funInterface/resolveFunInterfaceWithoutMainMethod.fir.kt

@@ -1,4 +1,4 @@
-fun interface IsolatedFunFace {
+<!FUN_INTERFACE_WRONG_COUNT_OF_ABSTRACT_MEMBERS!>fun<!> interface IsolatedFunFace {
 }
 
 typealias FunAlias = IsolatedFunFace
@@ -9,4 +9,4 @@ fun callIsolatedFunFace() {
     referIsolatedFunFace(<!UNRESOLVED_REFERENCE!>IsolatedFunFace<!> {})
     referIsolatedFunFace(<!UNRESOLVED_REFERENCE!>FunAlias<!> {})
     referIsolatedFunFace(<!ARGUMENT_TYPE_MISMATCH!>{}<!>)
-}
+}