Swift Package Manager [WIP]

[chrisballinger]

Testing notes:

• cd /path/to/opencv
• First build the xcframework python platforms/apple/build_xcframework.py platforms/apple/xcframework-build/ or place your prebuilt opencv2.xcframework at platforms/apple/xcframework-build/opencv2.xcframework
• swift build

Currently dealing with some interface issues with the existing Swift module from the objc module:

/Users/chrisbal/Documents/opencv/.build/x86_64-apple-macosx/debug/opencv2.framework/Modules/opencv2.swiftmodule/x86_64-apple-macos.swiftinterface:676:81: error: ambiguous type name 'Rect' in module 'opencv2'
  public func detectMultiScale(img: opencv2.Mat, foundLocations: inout [opencv2.Rect], foundWeights: inout [Swift.Double], hitThreshold: Swift.Double)
                                                                        ~~~~~~~ ^
opencv2.Rect:1:12: note: found candidate with type 'Rect'
open class Rect : NSObject {
           ^
Darwin.Rect:1:15: note: found candidate with type 'Rect'
public struct Rect {
              ^

I think one possible solution could be to remove the Swift stuff from the objc module and only include it via the Swift Package, but it would be a breaking change for consumers of the existing module.

TODO:

• Fix swift module interface so it compiles
• Get tests in modules/core/misc/objc/test to run via swift test

Resolves opencv#18398

[colejd]

Related: opencv#18843