use linear space and default intensity to 1.0 in EnvironmentMapLight::solid_color

[atlv24]

Objective

• solid_color returned envmap lights that looked black

Solution

• set intensity to 1.0
• also make sure to use proper color space (linear)

Testing

• tested in reflection_probe example

[DGriffin91]

I think it would be good to expose the intensity as a param so setting it feels similar to doing

EnvironmentMapLight {
    diffuse_map: asset_server.load("environment_maps/pisa_diffuse_rgb9e5_zstd.ktx2"),
    specular_map: asset_server.load("environment_maps/pisa_specular_rgb9e5_zstd.ktx2"),
    intensity: 250.0,
    ..default()
},

or

GlobalAmbientLight {
    color: Color::WHITE,
    brightness: 250.0,
    ..default()
}

Or add a method to set it on EnvironmentMapLight so you could do EnvironmentMapLight::hemispherical_gradient().intensity(250.0) or whatever.

[DGriffin91]

Not tied directly to this PR but the initial one got merged before I had a chance to test. Anyway I think this needs to be a bit higher resolution to be generally usable since only bilinear sampling is used:

[DGriffin91]

If hemispherical_gradient_cubemap() was pub it would also let you use the same HDRI for the SkyBox and EnvMap

let cubemap = assets.add(Self::hemispherical_gradient_cubemap(
    Color::linear_rgb(2.0, 2.0, 2.0),
    Color::linear_rgb(1.0, 1.0, 1.0),
    Color::linear_rgb(0.0, 0.0, 0.0),
));
[...]
EnvironmentMapLight {
    diffuse_map: cubemap.clone(),
    specular_map: cubemap.clone(),
    intensity: 1000.0,
    ..default()
},
Skybox {
    image: cubemap.clone(),
    brightness: 1000.0,
    ..default()
}