Xcode Test Results as Bitrise environment variables

[markst]

Checklist

• I've read and followed the Contribution Guidelines
• step.yml and README.md are updated with the changes (if needed)
• Updated bitrise.yml with necessary environment variables

Version

Context

This PR adds functionality to parse .xcresult files and set the number of tests passed and failed as environment variables (BITRISE_XCODE_TESTS_PASSED_COUNT and BITRISE_XCODE_TESTS_FAILED_COUNT).

Resolves: https://discuss.bitrise.io/t/surface-xcode-test-results-as-bitrise-output-variable/1630

Changes

• Added structs TestSummary and TestResults to main.go for parsing .xcresult JSON output.
• Added ExportTestResults method in main.go to parse the .xcresult file and set the environment variables for the number of tests passed and failed.
• Updated ExportXCResultBundle method to call ExportTestResults.

Investigation details

Alternative solutions involved parsing the .xcresult files using different tools, but xcresulttool was chosen for its reliability and ease of use with Xcode-generated files.

Decisions

• Decided to use xcresulttool for parsing .xcresult files.
• Chose to add environment variables BITRISE_XCODE_TESTS_PASSED_COUNT and BITRISE_XCODE_TESTS_FAILED_COUNT to provide clear metrics on test results.

[markst]

Will need to add tests to validate this, I wonder if we have an .xcresult file on the repo can validate against?

[markst]

teameh/bitrise-step-bitbucket-server-post-build-status#10