Replace extern with external in interop error messages

compiler/ballerina-lang/src/main/java/org/wso2/ballerinalang/compiler/bir/codegen/interop/ExternalMethodGen.java

@@ -240,7 +240,7 @@ public static BIRFunctionWrapper createExternalFunctionWrapper(boolean isEntry,
                                                                            isEntry, jvmPackageGen.symbolTable);
                 }
             } else {
-                throw new BLangCompilerException("cannot find full qualified class name for extern function : " +
+                throw new BLangCompilerException("cannot find fully qualified class name for external function : " +
                                                          pkgName + birFunc.name.value);
             }
         }

tests/jballerina-unit-test/src/test/java/org/ballerinalang/test/javainterop/basic/NegativeValidationTest.java

@@ -19,6 +19,7 @@
 
 import io.ballerina.runtime.api.values.BFuture;
 import io.ballerina.runtime.api.values.BTypedesc;
+import org.ballerinalang.compiler.BLangCompilerException;
 import org.ballerinalang.test.BAssertUtil;
 import org.ballerinalang.test.BCompileUtil;
 import org.ballerinalang.test.CompileResult;
@@ -558,4 +559,11 @@ public void testAbstractClassInstantiationError() {
                         " ''org.ballerinalang.nativeimpl.jvm.tests.Interface' is abstract, and cannot be instantiated'",
                 23, 1);
     }
+
+    @Test(expectedExceptionsMessageRegExp = ".*cannot find fully qualified class name for external function : .*",
+            expectedExceptions = BLangCompilerException.class)
+    public void testClassNameForExternalFunctionNotFound() {
+        String path = "test-src/javainterop/negative/external_function_class_name_not_found.bal";
+        BCompileUtil.compile(path);
+    }
 }

tests/jballerina-unit-test/src/test/resources/test-src/javainterop/negative/external_function_class_name_not_found.bal

@@ -0,0 +1,21 @@
+// Copyright (c) 2023, WSO2 LLC. (https://www.wso2.com) All Rights Reserved.
+//
+// WSO2 LLC. licenses this file to you under the Apache License,
+// Version 2.0 (the "License"); you may not use this file except
+// in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+function foo() {
+    function (typedesc<int> x) returns int fn1 = bar;
+}
+
+function bar(typedesc<int> y) returns y = external;