Re-implement cross platform copy and paste

[tauraamui]

macOS taken from Sokol:

_SOKOL_PRIVATE void _sapp_macos_set_clipboard_string(const char* str) {
    @autoreleasepool {
        NSPasteboard* pasteboard = [NSPasteboard generalPasteboard];
        [pasteboard declareTypes:@[NSPasteboardTypeString] owner:nil];
        [pasteboard setString:@(str) forType:NSPasteboardTypeString];
    }
}

_SOKOL_PRIVATE const char* _sapp_macos_get_clipboard_string(void) {
    SOKOL_ASSERT(_sapp.clipboard.buffer);
    @autoreleasepool {
        _sapp.clipboard.buffer[0] = 0;
        NSPasteboard* pasteboard = [NSPasteboard generalPasteboard];
        if (![[pasteboard types] containsObject:NSPasteboardTypeString]) {
            return _sapp.clipboard.buffer;
        }
        NSString* str = [pasteboard stringForType:NSPasteboardTypeString];
        if (!str) {
            return _sapp.clipboard.buffer;
        }
        _sapp_strcpy([str UTF8String], _sapp.clipboard.buffer, _sapp.clipboard.buf_size);
    }
    return _sapp.clipboard.buffer;
}

[linear]

LIL-82 Re-implement cross platform copy and paste