Support disabling window decorations in X11 and Win32

[jpcima]

Hi, this adds ability to hide the window captions.
It's a starting point to implement such things as popup menu widgets.

• On X11, it's using some Motif properties, which seems the widespread method from various toolkits.

• On Windows, it's the style WS_CAPTION, needing some particular care to set it on/off.
  It needs to recalculate the adjusted window size after setting the hint. I will preserve the former position of the window.

A detail: the window's drawable area has an offset between caption on/off on Windows, because the title bar's top-left is considered the rectangle's origin, unlike in X11.

Other: on Windows it still has the resize border, unless setting isResizable to false.

macOS to be implemented..

[falkTX]

What is the usecase or this?

[jpcima]

It's to create some popup menus in their distinct window, such as it's not limited to the drawing area.
eg. traditional menu, context menu, combo box

[falkTX]

So the window type does not change after it is created right?
If so, I would be prefer this to be a new parameter in the Window constructor, or better yet a new class that subclasses Window and calls its private methods as needed.
Adding 2 methods to the Window class that are only relevant to its creation doesn't seem nice. There is already a bit too much of that already

[falkTX]

Another reason to have it as a new class is that these kinds of windows cannot use parentId (for embed).
So a new class would not make that constructor method available at all.
And potentially a parent Window class is required, so that it can set transient hint or even modal stuff.
What do you think?

[jpcima]

So the window type does not change after it is created right?
If so, I would be prefer this to be a new parameter in the Window constructor, or better yet a new class that subclasses Window and calls its private methods as needed.

It does not have any need to change after creating.
By personal preference, I would have the subclass instead of introducing a Nth constructor argument.

And potentially a parent window is required, so that it can set transient hint or even modal stuff.

Judgind by the documentation, I think it should definitely have it.
https://tronche.com/gui/x/icccm/sec-4.html#WM_TRANSIENT_FOR

[jpcima]

Hmm, I believe there exists an anomaly in Windows code.
It does a forbidden operation according to the MSDN.

https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setwindowlongptra

Do not call SetWindowLongPtr with the GWLP_HWNDPARENT index to change the parent of a child window. Instead, use the SetParent function.