Update for changed .xcresult format in Xcode 11

[babbage]

Xcode 11 fundamentally changes the .xcresult file format. FBSnapshotsViewer would need to be updated in order to detect and parse test results in Xcode 11.

I'm taking a look at this to see how complex this is to resolve. Unsure whether I can commit to resolving this.

Example discussion of this issue in the context of a Fastlane tool here: https://github.com/fastlane-community/trainer/issues/32

[babbage]

I think it would be worth considering incorporating a dependency on XCResultKit to outsource parsing of these files, and thus hopefully outsource keeping up to date with future changes in .xcresult file format: https://github.com/davidahouse/XCResultKit