JS: use 'external' word instead of 'native' in diagnostic messages

See KT-20639

compiler/testData/diagnostics/testsWithJsStdLib/native/rtti/castToNativeInterface.kt

@@ -1,5 +1,5 @@
 external interface I
 
 fun box(a: Any, b: Any): Pair<I, I?> {
-    return Pair(<!UNCHECKED_CAST_TO_NATIVE_INTERFACE!>a as I<!>, <!UNCHECKED_CAST_TO_NATIVE_INTERFACE!>b as? I<!>)
+    return Pair(<!UNCHECKED_CAST_TO_EXTERNAL_INTERFACE!>a as I<!>, <!UNCHECKED_CAST_TO_EXTERNAL_INTERFACE!>b as? I<!>)
 }

compiler/testData/diagnostics/testsWithJsStdLib/native/rtti/checkForNativeInterface.kt

@@ -1,5 +1,5 @@
 external interface I
 
 fun box(a: Any, b: Any): Boolean {
-    return <!CANNOT_CHECK_FOR_NATIVE_INTERFACE!>a is I<!> && <!CANNOT_CHECK_FOR_NATIVE_INTERFACE!>b !is I<!>
+    return <!CANNOT_CHECK_FOR_EXTERNAL_INTERFACE!>a is I<!> && <!CANNOT_CHECK_FOR_EXTERNAL_INTERFACE!>b !is I<!>
 }

compiler/testData/diagnostics/testsWithJsStdLib/native/rtti/nativeInterfaceAsReifiedTypeArgument.kt

@@ -14,8 +14,8 @@ fun bar() {
     foo(C())
 
     val c: I = C()
-    <!NATIVE_INTERFACE_AS_REIFIED_TYPE_ARGUMENT!>foo(c)<!>
-    foo<<!NATIVE_INTERFACE_AS_REIFIED_TYPE_ARGUMENT!>I<!>>(C())
+    <!EXTERNAL_INTERFACE_AS_REIFIED_TYPE_ARGUMENT!>foo(c)<!>
+    foo<<!EXTERNAL_INTERFACE_AS_REIFIED_TYPE_ARGUMENT!>I<!>>(C())
 
-    <!NATIVE_INTERFACE_AS_REIFIED_TYPE_ARGUMENT!>C() + c<!>
+    <!EXTERNAL_INTERFACE_AS_REIFIED_TYPE_ARGUMENT!>C() + c<!>
 }

compiler/testData/diagnostics/testsWithJsStdLib/native/rtti/nativeInterfaceClassLiteral.kt

@@ -1,5 +1,5 @@
 external interface I
 
 fun box() {
-    println(<!NATIVE_INTERFACE_AS_CLASS_LITERAL!>I::class<!>)
+    println(<!EXTERNAL_INTERFACE_AS_CLASS_LITERAL!>I::class<!>)
 }

compiler/testData/diagnostics/testsWithJsStdLib/native/rtti/whenIsNativeInterface.kt

@@ -3,7 +3,7 @@ external interface I
 external interface J
 
 fun box(a: Any) = when (a) {
-    <!CANNOT_CHECK_FOR_NATIVE_INTERFACE!>is I<!> -> 0
-    <!CANNOT_CHECK_FOR_NATIVE_INTERFACE!>!is J<!> -> 1
+    <!CANNOT_CHECK_FOR_EXTERNAL_INTERFACE!>is I<!> -> 0
+    <!CANNOT_CHECK_FOR_EXTERNAL_INTERFACE!>!is J<!> -> 1
     else -> 2
 }