Closing dirty custom document calls revert after the view is disposed before onDidDispose is called

<!-- ⚠️⚠️ Do Not Delete This! bug_report_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- 🕮 Read our guide about submitting issues: https://github.com/microsoft/vscode/wiki/Submitting-Bugs-and-Suggestions --> <!-- 🔎 Search existing issues to avoid creating duplicates. --> <!-- 🧪 Test using the latest Insiders build to see if your issue has already been fixed: https://code.visualstudio.com/insiders/ --> <!-- 💡 Instead of creating your report here, use 'Report Issue' from the 'Help' menu in VS Code to pre-fill useful information. --> <!-- 🔧 Launch with `code --disable-extensions` to check. --> Does this issue occur when all extensions are disabled?: Yes/No <!-- 🪓 If you answered No above, use 'Help: Start Extension Bisect' from Command Palette to try to identify the cause. --> <!-- 📣 Issues caused by an extension need to be reported directly to the extension publisher. The 'Help > Report Issue' dialog can assist with this. --> - VS Code Version: 1.63.2 - OS Version: ArchLinux Reproduced both locally (with my own extension and with pawDrawEditor) and on github.dev (only with my own extension. didn't try to install pawDrawEditor on github.dev ...). Steps to Reproduce: 1. Create a dirty custom editor 2. Close it 3. revert on the document is called before the dispose on the view For a property implemented editor, this causes the document to attempt to update the view (most likely by sending a message) but will fail because the view is already destroyed, even though the extension hasn't be notified about this yet. The pawDrawEditor in the example didn't appear to have this issue (no error) only because the async call to readFile causes the onDidDispose to be called before the webview collection attempts to send the message. A benign change like the following, however, is enough to trigger this issue reliably. ```diff diff --git a/custom-editor-sample/src/pawDrawEditor.ts b/custom-editor-sample/src/pawD…