fix(coordinate_transform): use names from spec when constructing coordinate space transform

[chrisj]

Currently the use of the dimension index causes the next set spec to fail the validateDimensionNames check.

You can replicate the issue here by adding an additional output dimension here and reloading the page twice.

https://neuroglancer-demo.appspot.com/#!%7B%22dimensions%22:%7B%22x%22:%5B1.8e-8%2C%22m%22%5D%2C%22y%22:%5B1.8e-8%2C%22m%22%5D%2C%22z%22:%5B4.5e-8%2C%22m%22%5D%7D%2C%22position%22:%5B49263.15234375%2C49176.1328125%2C1694.5%5D%2C%22crossSectionScale%22:1.6791634573917904%2C%22projectionOrientation%22:%5B-0.00024565105559304357%2C-0.11311007291078568%2C0.00002710020635277033%2C0.9935824275016785%5D%2C%22projectionScale%22:131072%2C%22layers%22:%5B%7B%22type%22:%22image%22%2C%22source%22:%22gs://zheng_mouse_hippocampus_production/v2/img_aligned_sharded_18nm/%7Cneuroglancer-precomputed:%22%2C%22tab%22:%22source%22%2C%22name%22:%22img_aligned_sharded_18nm%22%2C%22visible%22:false%7D%5D%2C%22selectedLayer%22:%7B%22size%22:986%2C%22visible%22:true%2C%22layer%22:%22img_aligned_sharded_18nm%22%7D%2C%22layout%22:%224panel-alt%22%7D

The initial input names: [x', 'y', 'z', '']
Output names: ['x', 'y', 'z', "test'"]

On reload, set spec changes input names to [x', 'y', 'z',  3] and coordinateTransformSpecificationToJson changes the order to ['3', 'x', 'y', 'z'] because numerical properties are first and ordered from smallest to largest.

On second reload:
specInputNames = ['3', 'x', 'y', 'z']
newToSpecDimensionIndices = [1, 2, -1, 3]
Which results in newOutputNames = ['y', 'z', 'z', "test'"] and fails the validateDimensionNames check.

[chrisj]

Also I just noticed another issue, if you add two additional properties, it only creates one additional input space dimension so you end up with

Error parsing "source" property: Error parsing "transform" property: Error parsing "inputDimensions" property: Expected rank of 5, but received rank of: 4