xcode: make release configuration the default

[headupinclouds]

Similar to #724

Currently the Xcode iOS facefilter build will launch in debug mode by default when the ▶️ icon is used, which will be slow. It would be better if we could make an optimized/release configuration the default, as this will be the first user experience, and release vs debug distinctions may not be obvious.

[headupinclouds]

There is some recent activity in CMake related to experimental support for Xcode schemes 🎆

• https://cmake.org/cmake/help/git-stage/variable/CMAKE_XCODE_GENERATE_SCHEME.html
• https://gitlab.kitware.com/cmake/cmake/issues/17919

The INFO tab has these settings:

• XCODE_SCHEME_EXECUTABLE
• XCODE_SCHEME_ARGUMENTS
• XCODE_SCHEME_ENVIRONMENT

But there doesn't seem to be anything like "Build Configuration" yet. We would probably have to add XCODE_SCHEME_BUILD_CONFIGURATION, unless there is another trick for this.

As described here, it would probably have to run Release if we defined our own configuration types: -DCMAKE_CONFIGURATION_TYPES="Release" .