MeasurementList is ignored for some objects when importing from GeoJSON

[petebankhead]

Bug report

Describe the bug
See #835 from @jameshball

In summary, measurement lists are only included by PathObjectTypeAdapters when deserialising detection objects, as can be seen in the code from https://github.com/qupath/qupath/blob/v0.3.0/qupath-core/src/main/java/qupath/lib/io/PathObjectTypeAdapters.java#L412

A second, more subtle bug is that when measurement lists are retained, their type can be changed. This is not expected to have any major effect beyond efficiency, but could potentially be important in some situations.

To Reproduce
Run the following script:

def roi = ROIs.createRectangleROI(0, 10, 20, 30, ImagePlane.getDefaultPlane())
def annotation = PathObjects.createAnnotationObject(roi)
annotation.setName("Original")
annotation.setPathClass(getPathClass("My custom class"))
annotation.getMeasurementList().addMeasurement("First measurement", 1.0)
annotation.getMeasurementList().addMeasurement("Second measurement", -2.0)

def json = GsonTools.getInstance(true).toJson(annotation)

// Print original annotation, class and measurement list
println "ORIGINAL"
println annotation
println annotation.getPathClass()
println annotation.getMeasurementList().class
println annotation.getMeasurementList()
println "----------------"

// Print deserialized annotation, class and measurement list
def newAnnotation = GsonTools.getInstance().fromJson(json, PathObject)
println "FROM JSON"
println newAnnotation
println newAnnotation.getPathClass()
println newAnnotation.getMeasurementList().class
println newAnnotation.getMeasurementList()

The new annotation does not have any measurements in QuPath v0.3.0.

Moreover, switching to use PathObjects.createDetectionObject(roi) reveals that the measurements are retained, but the class of the measurement list is changed from FloatList to DoubleList - requiring more memory.

Expected behavior
As much information as possible is retained when serialising to/from GeoJSON.

Desktop (please complete the following information):

• QuPath v0.3.0