The 'EXPLORER' panel is opened if close one split tab

[v-xianya]

Storage Explorer Version: 1.34.0-dev (98)
Build Number: 20240508.1
Branch: rel/1.34.0
Platform/OS: Windows 10/Windows 11/Linux Ubuntu 22.04/MacOS Sonoma 14.4.1(Apple M1 Pro)
Architecture: x64/arm64/x64/arm64
How Found: Exploratory testing
Regression From: Previous release (1.33.1)

Steps to Reproduce

1. Expand one storage account -> Blob Containers.
2. Open one blob container -> Split the blob container tab.
3. Toggle sidebar by pressing Ctrl+B or clicking the first icon on the vertical toolbar.
4. Close one of the blob container tabs.
5. Check whether the EXPLORER panel is not opened.

Expected Experience

The EXPLORER panel is not opened.

Actual Experience

The EXPLORER panel is opened.

Additional Context

If switch to 'ACCOUNT MANAGEMENT' panel -> then close one split tab -> It will navigate to 'EXPLORER' panel.

[craxal]

This only happens if the last tab of a split panel is closed. The shell does not take into account that other tabs in other splits might be available to focus before focusing on the explorer panel.

Not the easiest fix, because the tab closing code is spread across several classes, and the code that adjusts focus isn't in a convenient spot. It's not a breaking change, and a subtle behavior, so I think this can wait till 1.35.0.

Bug was introduced here when fixing #7702: https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_git/StorageExplorer/pullrequest/531330

[MRayermannMSFT]

Revsisit if a user complains.