Add command line build flag to skip .ipa export for iOS exports

[phil-hudson]

Add command line build flag to skip .ipa export for iOS exports

Why?

When combining Godot with Fastlane, or other build pipelines, sometimes you need only the project built, but not the app ipa built.

For example, building just the project, and then running a manual xcbuild against the project afterwards has certain benefits:

• able to modify xc project files before build, e.g, certs, provisioning, build number bump
• Able to apply additional command line options to xcbuild command
• Allow build pipeline to pass in Fastlane, then run the ipa build separately afterwards

For implementation, it should be in the iOS export.cpp, read in an additional flag. If the flag is set, it skips the IPA build step

[phil-hudson]

PR up:

godotengine/godot#78641