fix(diagnostics): workaround Rollup duplicating error messages (#373)

* fix(diagnostics): workaround Rollup duplicating error messages

- per my investigation in the linked issues, it seems like Rollup has a bug where it duplicates some error message
  - this occurs when the error has a stack (or frame) which contains the error message itself
    - Rollup prints _both_ the error message _and_ the stack in that case, causing duplication

- this fix adds a workaround for this upstream Rollup bug
  - it detects if there is a stack and if the message is duplicated in the stack
    - if so, it removes the duplication in the stack
  - this workaround should be forward-compatible if this behavior is fixed upstream
    - this code should just end up re-throwing in that case (effectively a no-op)

* fix watch mode by spreading err

- apparently Rollup attaches several properties to the error object, including `watchFiles`
  - so removing them / not spreading causes watch to just stop working

here are some of the additional properties I logged out, for example:
```js
{
    id: '/project-dir/src/difference.ts',
    hook: 'transform',
    code: 'PLUGIN_ERROR',
    plugin: 'rpt2',
    watchFiles: [
      '/project-dir/src/index.ts',
      '/project-dir/tsconfig.json',
      '/project-dir/src/types.ts',
      '/project-dir/src/difference.ts'
    ]
  }
}
```

src/index.ts

@@ -253,6 +253,19 @@ const typescript: PluginImpl<RPT2Options> = (options) =>
 			return transformResult;
 		},
 
+		buildEnd(err)
+		{
+			if (!err)
+				return
+
+			// workaround: err.stack contains err.message and Rollup prints both, causing duplication, so split out the stack itself if it exists (c.f. https://github.com/ezolenko/rollup-plugin-typescript2/issues/103#issuecomment-1172820658)
+			const stackOnly = err.stack?.split(err.message)[1];
+			if (stackOnly)
+				this.error({ ...err, message: err.message, stack: stackOnly });
+			else
+				this.error(err);
+		},
+
 		generateBundle(bundleOptions)
 		{
 			self._ongenerate();