This functions very similarly to VSCode's pinned tab feature. To pin a
tab, you can right-click on it and select "Pin tab" from the context
menu. Once pinned, a tab will be fixed to the left-most edge of the tab
bar, in order of pinning. Pinned tabs can be dragged around like any
others. If you drag an unpinned tab into the pinned tabs section (any
index less than the highest-index pinned tab), it will be pinned. If you
drag a pinned tab out of the pinned tab section, it will be unpinned.
Pinned tabs' close button is replaced with a persistent pin button,
which can be clicked to unpin them. This adds an extra barrier to
accidentally closing a pinned tab. They can still be closed from the
context menu.
This was causing a crash on Windows because we were destroying a TabView
that was still parented to the window. Not sure why I couldn't repro
this on Mac...
This fixes a bug where closing the active tab would clean up the closed
tab view before switching to an un-closed tab view, putting the window
into an unrecoverable state. This also moves around some of the CloseTab
logic so that it's more standardized and reduces unnecessary
frontend-backend comms and DB writes
