[Wasm] Port external declaration checker to K2 (KT-56849)

Share common code with FirJsExternalChecker using
FirWebCommonExternalChecker

compiler/testData/diagnostics/wasmTests/jsInterop/nonAbstractMembersOfInterface.kt

@@ -0,0 +1,18 @@
+// FIR_IDENTICAL
+external interface I {
+    <!NON_ABSTRACT_MEMBER_OF_EXTERNAL_INTERFACE!>fun foo(): Unit<!> = definedExternally
+
+    val a: Int?
+        get() = definedExternally
+
+    var b: String?
+        get() = definedExternally
+        set(value) = definedExternally
+
+    <!NON_ABSTRACT_MEMBER_OF_EXTERNAL_INTERFACE!>val c: Int<!>
+        get() = definedExternally
+
+    <!NON_ABSTRACT_MEMBER_OF_EXTERNAL_INTERFACE!>var d: String<!>
+        get() = definedExternally
+        set(value) = definedExternally
+}