Simplify get_transform(), get_bounds(), get_resolution(), and get_extent()

[jnhansen]

Is your feature request related to a problem? Please describe.
The following methods are not currently very consistent in what information is used to extract the corresponding parameter:

• nd.warp.get_transform()
• nd.warp.get_bounds()
• nd.warp.get_extent()
• nd.warp.get_resolution()

Describe the solution you'd like
The most reliable information to determine the transform etc. is probably the coordinate arrays and should be used even if there is relevant metadata present.

The methods may optionally raise a warning if the coordinate arrays don't seem to match the values specified in the metadata.