Ensure that showOpenDialog returns correct file URI (#13208)

Use `URI.file` instead of manually reconstructing the URI from the received file path in plugin ext.
This ensures that directories or files that contain a hash are not wrongly added to the fragment component of the URI and aligns it with the expected behavior of VS Code.

Fixes #13074

Contributed on behalf of ST Microelectronics

packages/plugin-ext/src/plugin/dialogs.ts

@@ -41,7 +41,7 @@ export class DialogsExtImpl {
                 if (result) {
                     const uris = [];
                     for (let i = 0; i < result.length; i++) {
-                        const uri = URI.parse('file://' + result[i]);
+                        const uri = URI.file(result[i]);
                         uris.push(uri);
                     }
                     resolve(uris);