This PR adds documentation for observable properties, which will then be pulled into the docs correctly once #1180 is merged. This is a first pass based on searching for definition of observable properties being defined as enums after lines ending with `Property = {`. If there are observable properties implemented that don't follow this pattern then they are not included.
I've added simple descriptions based on what I know or could easily figure out, there may be some properties (like preload) that are not correctly described.
I've also added `readonly` annotations where I knew that a property was readonly. I may have missed some readonly properties.
ol.layer.Base has a bunch of properties but I don't think it is exported so the documentation of these properties will not show up, so I added the documentation to ol.layer.Layer instead even though this isn't really where it should be documented.
The following functions are renamed:
getTransform -> getTransformForProjections
getTransformFromCodes -> getTransform
transform -> transformWithProjections
transformWithCodes -> transform
With this change, the faster functions that avoid projection look-up
have longer names and are used internally, whereas the slower but
friendlier short name functions are available for users.
