Add info about color and intensity to surface guide

[TimMonko]

References and relevant issues

depends on napari/napari#8909

Description

Adds information about how colors are handled in surface layers, especially as it relates to contrast and colormaps.
Adds info relevant to napari/napari#8909 where color controls are disabled when vertex_colors is passed.
I tried also to clarify how omitting the vertex values resulted in 1s being used to color the surface, resulting in "white" and thus a bit of magic (to me) seemed to be involved in contrast controls and such. I still don't feel like I got the words out correctly.

[willingc]

Since there are several long components and one optional, changing to a bulleted list would reduce cognitive load for reader.

[willingc]

Suggested change

	Controls related to `contrast limits`, `auto-contrast`, `gamma`, and
	`colormap` are only available when the surface color is computed from
	`vertex_values`. If you provide `vertex_colors`, napari uses those colors
	When the surface color is computed from `vertex_values`, controls related to `contrast limits`, `auto-contrast`, `gamma`, and
	`colormap` are unavailable. If you provide `vertex_colors`, napari uses those colors

Is vertex_colors a vertex_value?

[TimMonko]

so this is IMO a bigger problem that I can address in the PR.
vertex_values is really the 3rd element of the data tuple, but it seems to be used throughout the docs and examples as if it were a real argument.
On the other hand, vertex_colors is an argument to Surface that overrides anything set in that third element of the data tuple.
I'll take another overall swing at the wording -- I think bulleting the tuple elements like above will probably help with this :)

[willingc]

No problem. I just didn't know the answer. Keep it simple now with just the bullets.

[willingc]

Consider a bullet list for sentences after the first.

Suggested change

	The data for a `surface` layer can be given as either a 2-tuple
	`(vertices, faces)` or a 3-tuple `(vertices, faces, vertex_values)`. The
	vertices are an `NxD` array of `N` vertices in `D` coordinates. The faces are
	an `Mx3` integer array of the indices of the triangles making up the faces of
	the surface. The optional vertex values are a length `N` list of scalar values
	to associate with each vertex for colormap-based rendering. If you omit
	`vertex_values`, napari fills them with ones, so the default underlying surface
	color is white.
	The data for a `surface` layer can be given as either a 2-tuple
	`(vertices, faces)` or a 3-tuple `(vertices, faces, vertex_values)`.
	- The vertices are an `NxD` array of `N` vertices in `D` coordinates.
	- The faces are an `Mx3` integer array of the indices of the triangles
	making up the faces of the surface.
	- The optional vertex values are a length `N` list of scalar values
	to associate with each vertex for colormap-based rendering.
	If you omit `vertex_values`, napari fills them with ones, so the default underlying surface color is white.

[brisvag]

Actually, surfaces values can be n-dimensional:

https://github.com/napari/napari/blob/93ef1fbc8de2758fd1b381a5ef7e5508323547a4/src/napari/layers/surface/surface.py#L55-L58

[brisvag]

same here as above.