How to use bridging header in a Swift Package?

I am trying to write a wrapper package for InputMethodKit.
This includes force-exposing certain internal symbols of IMKCandidates:

#import <InputMethodKit/InputMethodKit.h>

@interface IMKCandidates(IMKCandidatesExploit) {}

- (unsigned long long)windowLevel;
- (void)setWindowLevel:(unsigned long long)level;
- (BOOL)handleKeyboardEvent:(NSEvent *)event;
- (void)setFontSize:(double)fontSize;

@end

However, I don't have a clue how to do this in a Swift Package.