Cursor_type property to use standard cursors

[PapyChacal]

Issue description

See #1049

Solution description

I added a cursor_type property. It takes value in a CursorType enum, and have four values representing cursor type at the moment, as well as CT_hidden, which replaces the cursor_hidden property, and CT_custom, which tells Panda to use cursor_filename instead.

I tried to replace every use of the cursor_hidden property accordingly. It seems to work alright on X11 and Win32, but I have doubts about the cocoa implementation as I don't have access to a macOS environment. This should break some existing use of the Panda3D API, as all the cursor_hidden-related functions are removed.

Checklist

I have done my best to ensure that…

• …I have familiarized myself with the CONTRIBUTING.md file
• …this change follows the coding style and design patterns of the codebase
• …I own the intellectual property rights to this code
• …the intent of this change is clearly explained
• …existing uses of the Panda3D API are not broken
• …the changed code is adequately covered by the test suite, where possible.

Notes

The way cursor_type and cursor_filename (and eventually cursor_hidden if it should instead be kept) still is to be discussed.

Before integrating this, the offered cursors should be discussed too. I used the following sources to see which cursors were exposed by which platform:

• X11 : https://tronche.com/gui/x/xlib/appendix/b/
• Win32 : https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-loadcursora
• Cocoa : https://developer.apple.com/documentation/appkit/nscursor

As one can see, those platforms offer different cursors. So for this draft, I simply used the set of cursors which clearly were the same on every platform (this reduces to default arrow, open hand, text beam, and crosshair...)

I could include some more with fallbacks: for example, Win32 and Cocoa both offer bidirectional horizontal and vertical resizing cursors, but X11 only offers unidirectional versions. I could make panda offer a unidirectional cursor_type and fall back to the bidirectional one in this case)
I could offer a union of those cursor types too, and return a flag or print a Warning or whatever if a platform doesn't support the asked type?
Finally, Panda could offer its own cursor theme, to get a consistent look and behavior on every platform.
Any other idea is welcome!

[codecov]

Codecov Report

Merging #1061 (5d6df28) into master (e83657f) will decrease coverage by 0.03%.
The diff coverage is 4.44%.

@@            Coverage Diff             @@
##           master    #1061      +/-   ##
==========================================
- Coverage   15.70%   15.67%   -0.04%     
==========================================
  Files        3708     3715       +7     
  Lines      357820   358350     +530     
==========================================
- Hits        56203    56167      -36     
- Misses     301617   302183     +566     

Impacted Files	Coverage Δ
panda/src/cocoadisplay/cocoaGraphicsWindow.mm	6.87% <0.00%> (-0.03%)	⬇️
panda/src/display/graphicsWindow.cxx	26.21% <ø> (-0.28%)	⬇️
panda/src/x11display/x11GraphicsWindow.cxx	0.00% <0.00%> (ø)
panda/src/display/windowProperties.I	54.46% <22.22%> (-2.12%)	⬇️
panda/src/display/windowProperties.cxx	48.80% <33.33%> (-0.72%)	⬇️
panda/src/linmath/lmatrix4_src.I	43.03% <0.00%> (-11.55%)	⬇️
dtool/src/dtoolbase/dtoolbase.h	57.14% <0.00%> (-9.53%)	⬇️
panda/src/linmath/lvecBase2_src.I	35.01% <0.00%> (-1.57%)	⬇️
panda/src/mathutil/boundingVolume.cxx	33.57% <0.00%> (-1.43%)	⬇️
panda/src/express/multifile.I	20.72% <0.00%> (-1.40%)	⬇️
... and 68 more

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[rdb]

I see this is still marked Draft, is this ready to receive review and feedback?