Until now, we relied on WM_SIZING to ensure that the island is not
downsized below minimal allowed dimensions. However, on some occasions
WM_WINDOWPOSCHANGED, e.g. when anchoring a window to the top/bottom of
the screen. This message will use dimensions obtained from
WM_GETMINMAXINFO. Until now we didn't override this value, falling back
to the defaults. As a result we got an inconsistent behavior (at least
when attaching the anchor).
I added logic very similar to the one we use in IslandWindow::_OnSizing
to the MINMAXINFO handler: snap the client area, add non client
exclusive are, consider DPI along the computation.
## Validation Steps Performed
* Manual testing of minimizing, maximizing, resizing, attaching
different anchors, etc.
Closes#8026
e3fcfccc52