Fix doc build (alternative)

Attempt to fix doc build failure introduced with matplotlib#25272.

I suspect this is sphinx scoping: matplotlib#25272 reused methods
like `Axes.set_xbounds` to generate documentation for Axes3D. However,
a see also of invert_xaxis only searches within the same module (or
class), and invert_xaxis is not documented for Axes3D. This PR
attempt to explicitly document the missing methods for Axes3D.

Author: timhoffm

doc/api/toolkits/mplot3d/axes3d.rst

@@ -98,6 +98,10 @@ Axis limits and direction
    get_zlim
    set_zlim
    get_w_lims
+   invert_xaxis
+   xaxis_inverted
+   invert_yaxis
+   yaxis_inverted
    invert_zaxis
    zaxis_inverted
    get_xbound