Window sizing coherency

Nobody has claimed this yet.

When giving druid a window size (e.g. `window_size` or `with_min_size`) what is the expected result? Does that size include OS-styling (title bar and other borders) or is that size meant only for druid-addressable drawing area?

I think having it mean only the addressable drawing area makes the most sense if we want to achieve pixel perfect designs across platforms.

I tested macOS and Windows, haven't looked at Linux yet. On macOS the druid window size does determine the drawing area :+1: but on Windows the drawing area will be smaller because all the OS borders have to fit within the size constraints. :confused:

I think it is possible to change the behavior on Windows, perhaps with [AdjustWindowRect](https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-adjustwindowrect) and friends.

Start by reproducing the behavior of `window_size` and `with_min_size` on macOS and Windows, then compare the drawing area with the full window size; Linux is also mentioned as untested. Read the Windows sizing path around `AdjustWindowRect` and determine whether the API should consistently measure the Druid-addressable drawing area. Done means the sizing semantics are defined and behavior is consistent across platforms.

Written by the indexing model from the issue text.