Add tab-view versions of panel-views

[tyler-dot-earth]

Is your feature request related to a problem? Please describe. Several views in Dendron are "panel-only views" (unsure of correct term), including:

• Backlinks
• Dendron tree view
• Outline (unsure if part of Dendron project)

These "panel-views" are only usable in "panels" -- meaning that:

• There are limited ways to lay them out (basically just left/right/bottom bars)
• They cannot be opened/rearranged like tabs (file contents, graphs) can

Describe the solution you'd like

• I'd like to be able to place Backlinks, Dendron tree view, and Outline wherever I'd like
• The most straightforward way of doing :point_up_2: this feels like just allowing/duplicating the "panel-only views" in tabs.

Describe alternatives you've considered n/a

Additional context n/a

[kevinslin]

Outline is builtin to VSCode, the other two parts we control. The vscode term is tree views.

For laying them out in panels, VSCode has a separate notion for tree views (panes) and editor views (tabs). Backlinks and the Dendron tree view are implemented as tree views. It would be possible to port them over to an editor view but that would require non-trivial work. Going to classify as a power feature initiative and evaluate the implementation around the end of year