Expose programmatic context provider registration

[samelhusseini]

Description

This allows vscode extension developers to create an extension that depends on the continue.continue extension and registers custom context providers programmatically.

The API uses the same interface for context providers configured in config.ts.

Sample use case:

class MyCustomProvider implements IContextProvider {

  get description(): ContextProviderDescription {
    return {
      title: "custom",
      displayTitle: "Custom",
      type: "normal",
    };
  }

  async getContextItems(
    query: string,
    extras: ContextProviderExtras
  ): Promise<ContextItem[]> {
    return [
      {
        name: "Custom",
        description: "Custom description",
        content: "Custom content",
      },
    ];
  }

  async loadSubmenuItems(
    args: LoadSubmenuItemsArgs
  ): Promise<ContextSubmenuItem[]> {
    return [];
  }
}

const customProvider = new MyCustomProvider();
const continueExt = vscode.extensions.getExtension("continue.continue");
const continueApi = continueExt?.exports;
continueApi?.registerCustomContextProvider(customProvider);

Related #1041

• The base branch of this PR is preview, rather than main

[sestinj]

This looks great! Code is written cleanly, and as I've thought about it more allowing this makes a lot of sense. Will look to merge early this week after I've gotten a refactor into preview first