Add specular occlusion documentation to StandardMaterial3D tutorial

[LunaCapra]

This adds documentation for both the "Disable Specular Occlusion" toggle as well as bent normal maps.

• Production edit: See Add support for bent normal maps for specular occlusion and indirect lighting godot#89988
  and Add specular occlusion from ambient light godot#106145.

[Calinou]

This is a bit large for the documentation. Here's a version compressed to 264 KB:
spatial_material_bentnormals.zip

It's very slightly lossy (WebP at quality 100 and preprocess dithering enabled to reduce banding), but is more than twice as small.

[hsvfan-jan]

I think this could be zoomed or cropped in way more, so that it's easier to focus on the differences. Especially on smaller screens this helps

[Calinou]

Suggested change

	* The bent normal map needs to use the X+, Y+ and Z+ coordinates, this is
	known as OpenGL style. If you've imported a material made to be used with
	another engine it may be DirectX style, in which case the bent normal map
	needs to be converted so its Y axis is flipped.
	* The bent normal map needs to use the X+, Y+ and Z+ coordinates, which is
	known as OpenGL-style. If you've imported a material made to be used with
	another engine, it may be DirectX-style. In this case, the bent normal map
	needs to be converted so its Y axis is flipped. This can be achieved by
	checking **Normal Map Invert Y** in the Import dock.

[LunaCapra]

Normal Map Invert Y in the import settings seems to be marked as deprecated in v4.5 dev5 and it says that the same result can be achieved by setting the green channel mapping to inverted green instead. Should I document that instead?

[Calinou]

Yes, I'd point to the new setting.

[clayjohn]

Content looks good to me

[Calinou]

Looks good to me.

We should probably include instructions on baking bent normal maps from various programs in a future PR, as the process for doing so is much less standardized (and less well-documented) than standard normal maps.