[core] Add more missing implementations to SDL

[ghost]

Changes

1. Adds ShowCursor implementation (R469-R471).
2. Adds HideCursor implementation (R477-R479).
3. Adds EnableCursor implementation (R485-R486).
4. Adds DisableCursor implementation (R494).
5. Adds SetClipboardText implementation (R455).
6. Adds GetClipboardText implementation (R459, R462).
7. Adds SetMouseCursor implementation (R65, R182-R196, R560-R563, R819).
8. Adds SetWindowFocused implementation (R335).
9. Adds GetMonitorPhysicalWidth implementation (R409-R425).
10. Adds GetMonitorPhysicalHeight implementation (R431-R447).
11. Adds GetWindowHandle implementation (R341).
12. Adds SetGamepadMappings implementation (R575).

Notes

• I don't have a joystick/controller here right now, so I couldn't test SetGamepadMappings.

Environment

Tested this changes successfully on Linux (Ubuntu 22.04 64-bit, gcc 11.2.0) with SDL2 (2.28.4).

Edits

1: added line marks.
2, 3, 4, 5, 6: added more implementations.

[ghost]

@raysan5 I think it's ready for merging. 👍

[raysan5]

@ubkp Great! Thanks for the additions! 👍🙂