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/package.json

@@ -13,6 +13,7 @@
     "diffCommand",
     "contribMergeEditorToolbar",
     "contribViewsWelcome",
+    "editSessionIdentityProvider",
     "scmActionButton",
     "scmSelectedProvider",
     "scmValidation",
@@ -24,6 +25,7 @@
   ],
   "activationEvents": [
     "*",
+    "onEditSession:file",
     "onFileSystem:git",
     "onFileSystem:git-show"
   ],