Toggle side bar visibility has issues when `registerWebviewViewProvider` with `retainContextWhenHidden` is used

<!-- ⚠️⚠️ 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 <!-- 🪓 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: 1.67.2 - OS Version: macOS 12.3 **Issue:** When using a custom webview panel in combination with another webview. There is a weird issue going on when toggling the sidebar its visibility using the `View: Toggle Primary Side Bar Visibility` command (`cmd+b`). In some cases it does not open the panel, it immediately closes again. In other cases, it is the other way around. Here is a video of what is happening: https://user-images.githubusercontent.com/2900833/172593687-4bfec844-d3a7-4494-bf5e-48030bbb23a8.mp4 This issue only occurs when the `retainContextWhenHidden` is set to `true` for the activity bar panel webview. **Steps to Reproduce:** To make it easier to test it out, I started from the [webview-view-sample](https://github.com/microsoft/vscode-extension-samples/blob/main/webview-view-sample) and added the cat webview. 1. Clone the following sample repo: `https://github.com/estruyf/vscode-webview-issue` 2. Run the sample 3. Open the `Calico Colors` activi…