Swift Package Manager support for CordovaLib

[dpogue]

Platforms affected

iOS

Motivation and Context

This adds a Package.swift file to allow installing the CordovaLib library through Swift Package Manager.

This also cleans up our Cocoapods spec file to remove the need to explicitly list each header.

Description

Swift Package Manager requires all the public headers to be in an include folder, so all the headers from Classes/Public were moved to include/Cordova.

Also got rid of the precompiled header because SwiftPM doesn't know how to do that, and we were only precompiling Foundation and UIKit.

Xcode 13 also adds a new warning when framework headers are used with relative imports "myfile.h" rather than framework imports <myfile.h>. I've cleaned up the imports for all the public headers. (Note: some of the plugins use private headers, which must retain the relative import syntax)

Testing

• Tested creating a new Swift project in Xcode, adding CordovaLib using SwiftPM and compiling successfully
• Tested creating a new Objective C project in Xcode, adding CordovaLib using Cocoapods as a dynamic library and compiling successfully
• Tested creating a new Objective C project in Xcode, adding CordovaLib using Cocoapods as a static library and compiling successfully
• Existing test suite passes

Checklist

• [x] I've run the tests to see all new and existing tests pass

[codecov-commenter]

Codecov Report

Merging #1154 (fc931bf) into master (4c81363) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1154   +/-   ##
=======================================
  Coverage   74.86%   74.86%           
=======================================
  Files          13       13           
  Lines        1723     1723           
=======================================
  Hits         1290     1290           
  Misses        433      433           

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