Enable dragging tabs between windows

[zadjii-msft]

Behold, the penultimate chapter in the saga of tear-out! This significant update bestows upon the user the power to transport tabs betwixt Terminal windows. Alas, the drag and drop capabilities of TabView are not yet refined, so this PR primarily concerns itself with the intricacies of plumbing. When a tab is extracted and deposited elsewhere, it is necessary to have the recipient make an inquiry to the Monarch, who in turn will beseech the sender to transmit the tab content, akin to the act of moving a tab. Curious it may seem, but the method has proven effective.

The penultimate tear-out PR. This PR enables the user to move tabs from one Terminal window to another. The TabView drag/drop APIs have some rough edges, so this PR is mostly plumbing. When a tab is drag/dropped, we need to get the recipient to ask the Monarch to ask the sender to send the tab content, like a MoveTab action. Wacky, but it works.

There's a LONG tail of UX gaps. Those I'm going to track in #14900. It is more valuable for us to merge this now than to figure out workarounds immediately.

The next PR will be the last main PR in this saga - in which we enable dragging a tab out of the window and dropping to create a new window.

• Closes Add support for tab tearoff and tab merge #1256
• Related to Scenario: Windows Terminal 2.0 Process Model Improvements #5000
• Follow-ups get to go in [MEGATHREAD] Tab drag/drop/tear-out gaps #14900

Detailed description

As I mentioned, it's mostly plumbing. The order that we get tab drag events is... unfortunate... for our use case. So we do a lot of sending RequestReceiveContentArgs up and down between windows, just to communicate who the tab was dropped on to whomever the tab was dragged from.

There's a diagram for this that I originally put in #5000 (comment):

sequenceDiagram
    participant Source
    participant Target
    participant Monarch

    Note Left of Source: _onTabDragStarting
    Source --> Source: stash dragged content
    Source --> Source: pack window ID into DataPackage

    Source ->> Target: Drag tab
    Note right of Target: _onTabStripDragOver
    Target ->> Target: AcceptedOperation(DataPackageOperation::Move)
    
    Source --> Target: Release mouse (to drop)
    
    Note right of Target: _onTabStripDrop
    Target --> Target: get WindowID from DataPackage
    Target -) Monarch: Request that WindowID sends content to us<br>RequestRecieveContent
    Monarch -) Source: Tell to send content to Target.Id<br>RequestSendContent, SendContent
    Source --> Source: detach our content
    Source -) Monarch: RequestMoveContent(stashed, target.id)
    Monarch -) Target: AttachContent(stashed)

    # Target -->> Source: 
    # Note Left of Source: TabViewTabDragStartingEventArgs<br>.OperationCompleted
    # Note Left of Source: _onTabDroppedCompleted

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Really really though, let's try to avoid nits about the UX at this time. This PR works with what we've got. Mail threads are percolating. I've got 19 chapters worth of Hobbit branch names to use for those follow ups.

[DHowett]

Once this retargets to main, build cycle required!

[patrikhuber]

Really cool to see the progress of this! May I ask, what's the approximate timeframe of seeing this in the Terminal if installed from the Windows Store?

[zadjii-msft]

@patrikhuber It'll probably be a while. We did have to rewrite the entire process model of the Terminal to support this. This will likely result in a long tail of edge cases that we want to iron out before shipping. Fortunately, I think the bot is still working for releases, so when this does finally go out, the bot will post here (and in #1256)

[patrikhuber]

Thank you Mike, I understand! I might be tempted then to try the GitHub release when it's available :-).

Thanks a lot for all the amazing work on Windows Terminal!

[sylph520]

Finally, really looking forward to the release of this feature, thanks mate.