Saving as on restored custom editor triggers spurious save confirmation

<!-- ⚠️⚠️ 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 and no (it's happens for custom editors). <!-- 🪓 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. Open a custom editor (the pawDrawEditor in the custom editor example works) 2. Make the document dirty (do some edit) 3. Reload vscode (without this the issue wasn't triggered) 4. Now if the custom editor is implemented correctly the same dirty state should have been restored (the pawDrawEditor does this correctly apart from not handling the untitled data case) 5. Do save-as on the document, pick a filename and save it 6. After confirming the file name, a new window will open for the new document (which is expected), but there'll also be a confirmation for whether the old document should be saved. The confirmation-before-close in the last step should not happen and indeed it doesn't happen if t…