Add precompiled xcframework binary option for SPM

[woohyunjin06]

Background

• When using FlexLayout with SPM, developers need to manually add FLEXLAYOUT_SWIFT_PACKAGE=1 to the GCC_PREPROCESSOR_DEFINITIONS for each target.
  This can cause inconvenience when creating and distributing other Swift Packages that depend on FlexLayout.
• This may cause unexpected issues when building with some third-party build systems.
  (In my case, issues occurred during a build with Tuist.)

In order to simplify this setup process, I proposed to offer a precompiled binary.

Changes

• Added a precompiled xcframework binary for FlexLayout that can be utilized through the binaryTarget property of Swift Package.
• Removed one of the redundantly declared postfix operator % statements to apply BUILD_LIBRARIES_FOR_DISTRIBUTION(Already declared in Percent.swift)
• Added a shell script that creates an XCFramework.

Related

• ABI stability swift evolution support for different swift versions #220
• 'YGEnums.h' file not found - When adding FlexLayout as dependency of another Swift Package. #219

[lucdion]

@OhKanghoon has opened this PR removing the need to define FLEXLAYOUT_SWIFT_PACKAGE.
Do you still think that your change is useful?

[woohyunjin06]

@lucdion Hi, I saw his PR too, and I think that can give users a better experience, so I don't think this PR is necessary if that PR is merged

[lucdion]

Thanks