Feature/glam cross constants

[pine-free]

Objective

Fixes #21333

Solution

This PR introduces several new constants for Dir2 and Dir3,
providing convenient shorthands for popular directions on a grid, such as:

• All the cardinal directions
• All diagonals
• All neighboring directions (cardinals + diagonals)

Testing

Changes were not tested via autotests, but I did check my math to make sure I didn't mess up.

You can look at the changed files and make sure that the constants contain the directions they are supposed to

Showcase

For example. if you have a grid and wish to get all neighboring cells on it,
you don't have to define the directions yourself and can do the following

let valid_positions = Dir2::ALL_NEIGHBORS.iter().filter_map(|offset| {
    grid.get(current_position + offset)
}.collect();

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[IQuick143]

This seems a bit weird, since an f32 can't hold more than about 7 digits of precision, but I don't know if there's maybe another reason to want an extra-precise constant definition.

[pine-free]

these excessively long definitions are copied from the rust std::f32::consts, but I'm unsure why they would be there in the first place

[pine-free]

i propose to keep this definition for now for the sake of consistency with the rust stdlib, so that when the FRAC_1_SQRT_3 gets stabilized we can just switch over to that and be certain that there's no weird behavior from unexpected changes

[IQuick143]

The documentation here is a little confusing, from the comment I understood that this is a diagonal between two cardinal directions, like a diagonal between X and Y, but it's diagonals between triplets of cardinal directions. So it's directions pointing towards the vertices of a cube centered at the origin / the main diagonals of such a cube.

[pine-free]

done

changed the documentation to reflect that these are directions to vertices

the directions between 2 lines are represented in the ALL_EDGES group

[IQuick143]

Nitpick: Neighborhoods aren't a standardised concept, so I think it would be good to specify it's in a 3x3 neighboorhood. Similarly for the 3d case specify a 3x3x3 neighboorhood.

[pine-free]

done

annotated the ALL_NEIGHBORDS collections with a "on a cube/square grid in a 3x3(x3) neighborhood"

[IQuick143]

This isn't all neighbors in a 3x3x3 range, it's the directly adjacent ones coresponding to 6 faces of a cube + the ones corresponding to the 8 vertices of a cube, but then there's missing 12 neighbors which correspond to the edges of a cube (which are closer than the corner ones, so it imho doesn't make sense to not include them). Overall there should be 26 of them (Since 3x3x3 = 27 and we remove the center).

[pine-free]

ooh, thank you! missed that. will add later

I'm guessing we would want a definition for them as well, at least for consistency

[IQuick143]

Probably yeah.

[pine-free]

done

added the ALL_EDGES collection

[ChristopherBiscardi]

Thank you for working on this!