Add Clipboard handling

[UnGast]

Description

Adds clipboard text handling for available platforms.

Documentation

SDL

• https://wiki.libsdl.org/SDL_GetClipboardText
• https://wiki.libsdl.org/SDL_SetClipboardText
• https://wiki.libsdl.org/SDL_HasClipboardText

Apple

• macOS: https://developer.apple.com/documentation/appkit/nspasteboard
• iOS: https://developer.apple.com/documentation/uikit/uipasteboard

Source Impact

Additions only.

Checklist

• I've read the Contribution Guidelines
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (to the extent possible).
• I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexpected benchmark regressions.
• I've updated the documentation (if appropriate).

[UnGast]

Currently implemented: getClipboardText() on Platform and SDLPlatform. Maybe the way Platform works can be changed => use Protocols instead of forwarding functions manually?

[ctreffs]

Currently implemented: getClipboardText() on Platform and SDLPlatform. Maybe the way Platform works can be changed => use Protocols instead of forwarding functions manually?

Funny I just had this requirement recently :-) Will have a look at it

[ctreffs]

I've switched to a protocol based implementation, since this will provide more flexibility on other platforms.