Implement and adopt edit session identifier API proposal (#157733)

* Add canonical workspace identifier proposed API

* Use canonical id to store and resume edit sessions

* Add git extension workspace identity provider

* Fix warning incorrectly showing up

* Make auto resume behavior opt in

* * Create a separate service
* Accept WorkspaceFolder instead of URI
* Return string instead of object

* Make edit session restores resilient to provider registration races

* Introduce an activation event
* Activate contributing extension before using provider

* `CanonicalWorkspaceIdentity` -> `EditSessionIdentity`

* Show progress while resuming edit session

* Store edit session even if extension will take care of opening target workspace

* Address most of PR feedback

* `IEditSessionsWorkbenchService` -> `IEditSessionsStorageService`

* Unregister provider in renderer

* Split out proposal into new `editSessionIdentityProvider.d.ts`

* Fix bad merge

* Always show progress in window

* Convert URI schemes

extensions/git/src/editSessionIdentityProvider.ts

@@ -0,0 +1,38 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as path from 'path';
+import * as vscode from 'vscode';
+import { Model } from './model';
+
+export class GitEditSessionIdentityProvider implements vscode.EditSessionIdentityProvider, vscode.Disposable {
+
+	private providerRegistration: vscode.Disposable;
+
+	constructor(private model: Model) {
+		this.providerRegistration = vscode.workspace.registerEditSessionIdentityProvider('file', this);
+	}
+
+	dispose() {
+		this.providerRegistration.dispose();
+	}
+
+	async provideEditSessionIdentity(workspaceFolder: vscode.WorkspaceFolder, _token: vscode.CancellationToken): Promise<string | undefined> {
+		await this.model.openRepository(path.dirname(workspaceFolder.uri.fsPath));
+
+		const repository = this.model.getRepository(workspaceFolder.uri);
+		await repository?.status();
+
+		if (!repository || !repository?.HEAD?.upstream) {
+			return undefined;
+		}
+
+		return JSON.stringify({
+			remote: repository.remotes.find((remote) => remote.name === repository.HEAD?.upstream?.remote)?.pushUrl ?? null,
+			ref: repository.HEAD?.name ?? null,
+			sha: repository.HEAD?.commit ?? null,
+		});
+	}
+}