Migrate PerformanceTracker to 2.0

[tomcashman]

https://github.com/mini2Dx/mini2Dx-ve/blob/master/core/src/main/java/org/mini2Dx/core/util/PerformanceTracker.java

Public methods such as

getUsedMemory()
getAverageUpdateDuration()
etc.

Should become part of the PlatformUtils interface. PerformanceTracker itself can provide the render methods as static methods.

The following calls will probably need to be wrapped into the PlatformUtils interface for future runtimes:

System.nanoTime()
System.currentTimeMillis()
Runtime.getRuntime().totalMemory()
Runtime.getRuntime().freeMemory()