[sharanggupta]

FullColorRoundtrip and PixelDensityRoundtrip were split out of RoundtripTest without the Test suffix, and PngWriteForceTrueColorText has a typo in its suffix. None of these names match the default Surefire includes, so their 63 test cases never ran. This renames them to *Test, like BitmapRoundtripTest. They all pass, and the default mvn build passes.

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