FeatureSummary: Add unit tests

...y/FeatureSummaryFatalOnMissingRequiredPackages-result.txt

...y/FeatureSummaryFatalOnMissingRequiredPackages-stderr.txt

...y/FeatureSummaryFatalOnMissingRequiredPackages-stdout.txt

...ummary/FeatureSummaryFatalOnMissingRequiredPackages.cmake

...tureSummary/FeatureSummaryIncludeQuietPackages-stdout.txt

...e/FeatureSummary/FeatureSummaryIncludeQuietPackages.cmake

.../RunCMake/FeatureSummary/FeatureSummaryPurpose-stdout.txt

Tests/RunCMake/FeatureSummary/FeatureSummaryPurpose.cmake

Tests/RunCMake/FeatureSummary/FeatureSummaryTypes-stdout.txt

Tests/RunCMake/FeatureSummary/FeatureSummaryTypes.cmake

...ke/FeatureSummary/FeatureSummaryURLDescription-stdout.txt

...unCMake/FeatureSummary/FeatureSummaryURLDescription.cmake

Tests/RunCMake/FeatureSummary/FindBar.cmake

Tests/RunCMake/FeatureSummary/FindBaz.cmake

Tests/RunCMake/FeatureSummary/FindFoo.cmake

Tests/RunCMake/FeatureSummary/RunCMakeTest.cmake