Configuration + UI to remember extensions allowed to handle URIs

[dalongi]

Addresses issue #69166.

What

Extensions that offer frequently-used URI handlers present a tedious UX: every time the URI handler is invoked, the user has to manually confirm that the extension is allowed to do it.

This change addresses the problem in two ways:

• Add a configuration setting of extension ids to treat as confirmed.
• Add a checkbox to the confirmation. When checked, the extension id is stored locally and the user is not prompted again for URIs handled by that extension.
  

Manual Testing

General setup for testing URI handlers

• Launch VSCode pointing to the workspace for MyExtension (which has a URI Handler).
• F5 to launch VSCode running MyExtension. All testing is done in this VSCode window.
• URL to trigger MyExtension's URL handler: code-oss:///test/

Prompt behavior is not regressed

• Verify settings.json has no config entry for MyExtension
• Open MyExtension URL
• Verify the prompt is shown. Click "Open"
• Open MyExtension URL
• Verify the prompt is shown.

Valid configuration settings

• Open settings.json
• Start adding key "extensions.confirmed"
• Verify autocomplete suggests the key and has a description. Default value of [] is filled in.
  
• Open MyExtension URL
• Verify the prompt is shown.
• Update "extensions.confirmedUriHandlerExtensionIds" config to include the ID for MyExtension
• Verify no prompt is shown, URL is handled.
• Update "extensions.confirmedUriHandlerExtensionIds" config to remove the ID for MyExtension
• Verify prompt is shown.

Invalid configuration settings

• Update settings.json "extensions.confirmedUriHandlerExtensionIds" to invalid values: {"hello": "world"}, "hello world", [{}]
• Open MyExtension URL
• Verify prompt shows, no errors in console.

Checkbox setting

• Open MyExtension URL
• Verify the prompt is shown.
• Check the checkbox.
• Click "Open".
• Verify the URL is handled.
• Open MyExtension URL
• Verify NO prompt is shown.
• Verify the URL is handled.

[msftclas]

All CLA requirements met.

[mostafaeweda]

@joaomoreno any updates on this?

[joaomoreno]

Sorry for the delay... Thanks! 🍻