Allow QuickInput UIs to display near to the mouse-click that invoked them

[gjsjohnmurray]

#237534 means users can drag QuickInput to a position other than top-centre. The new position is then used for all subsequent QuickInputs.

I would like this feature to be extended so an extension displaying a QuickInput can signal that it should be displayed close to the coordinates of the user interaction that triggered it.

For instance the Git extension adds a StatusBarItem displaying the name of the current branch. Clicking on this is equivalent to invoking Git: Checkout to... from Command Palette (itself a QuickInput). When invoked from Command Palette it makes sense for the list of branches to appear in the same position as CP. But when invoked by clicking in the lower left corner of the window (i.e. the StatusBarItem) I think it would be better to display the subsequent QuickInput in that region of the screen.

Simulated by dragging the QuickInput after it appeared:

pinging @TylerLeonhardt @lszomoru