Rework how BlobExtensionPanelManager handles finding existing panel to open

Currently openBlobExplorer in BlobExtensionPanelManager saves all opened panels in a Map regardless of which TabPanel the panel is opened on (does not differentiate if the panel is opened in the left SplittableTabPanel or right SplittableTabPanel when there are more than one TabPanels). This is a problem because saving panels in this way is not congruent with the expected behavior of the "open" and "open to the side" commands of the BlobContainerExplorer.

When a container is opened using the "open" command, the expected behavior is to open a new tab in the current panel. If a tab currently exists for the same container, "open" should focus on that tab. When a container is opened using the "open to the side" command, the expected behavior is to open a tab in a split tab panel to the side. If a tab currently exists in the split tab panel to the side, the focus will be placed on that tab.

What currently happens is that "open" will always move focus to the tab of a container that already exists regardless of which tab panel the BlobContainerExplorer is in.

Instead PanelIdentifier should be reworked to take into account/track which TabPanel the newly created tab is opened from. That way BlobExtensionPanelManager can determine whether to open a new tab or show and existing tab within a specific tab panel.

Start with BlobExtensionPanelManager.openBlobExplorer and the PanelIdentifier implementation. Trace how the BlobContainerExplorer's "open" and "open to the side" commands identify existing tabs across the left and right SplittableTabPanel instances. Done means each command focuses an existing tab only within its intended panel, or opens a new tab there when none exists.