refactor error handling part 1 (#307)

- created `getErrorMessage` function which takes in an error string or any type of error object and returns the correct error message
- replaced `error.message` with `getErrorMessage` since `error` could be a string in some cases
- merged sendNotificationForError.ts with ErrorHandlingUtils.ts
- some minor refactoring

In part 2, I will make the following changes:
 - Make `Logger.logError` function take an error message string instead of an error object. This will reduce some redundancy where the `getErrorMessage` function is being called twice (the error object passed by the caller is already an error message).
 - Update every `TelemetryProcessor.traceFailure` call to make sure we pass in an error message instead of an error object since we stringify the data we send.

src/Explorer/Tree/StoredProcedure.ts

@@ -9,6 +9,7 @@ import * as TelemetryProcessor from "../../Shared/Telemetry/TelemetryProcessor";
 import Explorer from "../Explorer";
 import StoredProcedureTab from "../Tabs/StoredProcedureTab";
 import TabsBase from "../Tabs/TabsBase";
+import { getErrorMessage } from "../../Common/ErrorHandlingUtils";
 
 const sampleStoredProcedureBody: string = `// SAMPLE STORED PROCEDURE
 function sample(prefix) {
@@ -158,7 +159,7 @@ export default class StoredProcedure {
             sprocTab.onExecuteSprocsResult(result, result.scriptLogs);
           },
           (error: any) => {
-            sprocTab.onExecuteSprocsError(error.message);
+            sprocTab.onExecuteSprocsError(getErrorMessage(error));
           }
         )
         .finally(() => {