Add ios_get_build_number action

[spencertransier]

What does it do?

This action adds an action called ios_get_build_number to get the current build number from an xcconfig file. Because Day One iOS and Mac use the build number to name builds, this new action is needed for things like GitHub release names and tags.

How to test

1. In the bloom/DayOne-Apple repo, switch to the spencer/demo-get-build-number-action branch
2. Run bundle exec fastlane ios test_get_build_number_action
3. The output should be "The build number is 2392"
4. Run bundle exec fastlane mac test_get_build_number_action
5. The output should be "The build number is 1471"

Checklist before requesting a review

• Run bundle exec rubocop to test for code style violations and recommendations
• Add Unit Tests (aka specs/*_spec.rb) if applicable
• Run bundle exec rspec to run the whole test suite and ensure all your tests pass
• Make sure you added an entry in the CHANGELOG.md file to describe your changes under the approprioate existing ### subsection of the existing ## Trunk section.

[mokagio]

Have you considered passing the file as an argument?

See discussion in #380 and the work done in #445.

[spencertransier]

@mokagio Ready for re-review. It now uses an argument instead of the env variable

[mokagio]

I was surprised by this because key = value is a valid xcconfig syntax. Looking at the pre-existing, underlying implementation, I can see why this is required given that we manually parse the xcconfig files

release-toolkit/lib/fastlane/plugin/wpmreleasetoolkit/helper/ios/ios_version_helper.rb

Lines 286 to 302 in e4b28a4

	# Read the value of a given key from an `.xcconfig` file.
	#
	# @param [String] key The xcconfig key to get the value for
	# @param [String] filePath The path to the `.xcconfig` file to read the value from
	#
	# @return [String] The value for the given key, or `nil` if the key was not found.
	#
	def self.read_from_config_file(key, filePath)
	File.open(filePath, 'r') do |f|
	f.each_line do |line|
	line = line.strip()
	return line.split('=')[1] if line.start_with?("#{key}=")
	end
	end
	return nil
	end

We should be able to replace that bespoke logic with the API provided by the xcodeproj gem like we do in Jetpack and WordPress iOS:

version_config_path = File.join(PROJECT_ROOT_FOLDER, 'config', 'Version.internal.xcconfig')
versions = Xcodeproj::Config.new(File.new(version_config_path)).to_hash

[spencertransier]

It looks like @iangmaia already started working on using xcodeproj instead of the manual parsing: #451

I decided to implement this as-is and update it as needed after Ian's PRs are fully merged into the project.