Move axis setup from facet into coord.setup_ax

[iangow]

Upstream PR review item from has2k1#1059.

Source review comments:

• Added two new coordinate systems: coord_polar and coord_radial. has2k1/plotnine#1059 (comment)
• Added two new coordinate systems: coord_polar and coord_radial. has2k1/plotnine#1059 (comment)

Requested change:

• Move the functionality currently in facet.set_limits_breaks_and_labels into the coord class, probably as coord.setup_ax.
• Let coord subclasses override setup_ax completely or call super() and add coord-specific behavior.
• Remove now-unnecessary coord/facet helper methods once coord.setup_ax owns this behavior.

Review goal: give custom coord classes a clearer extension point and keep coord-specific behavior inside coord modules.

[iangow]

Addressed by commit 9c74855: Move axes setup to coord classes