Normalization error in image-based lighting

[jjhembd]

Our image-based lighting codes do not normalize the view vector, leading to (slightly) incorrect lighting calculations.

For example, in ImageBasedLightingStageFS,

vec3 proceduralIBL(...)
{
    vec3 v = -positionEC;
    vec3 n = normalEC;
    vec3 r = normalize(czm_inverseViewRotation * normalize(reflect(v, n)));
    float NdotV = abs(dot(n, v)) + 0.001;

NdotV should represent the cosine of the angle between normal and view vectors. But with v being unnormalized, NdotV can potentially be greater than 1 at normal incidence, and too large at angles between 0 and 90°.
The first line should read as follows:

    vec3 v = -normalize(positionEC);

There is a similar problem in the textureIBL function.

Here are a few images showing the impact of the error, as noticed while working on #11988.

Default environmental lighting (textureIBL), current code:

Default environmental lighting, corrected code. Note the additional light at the edges of the spheres in the right column, as well as a slightly more linear trend in brightness from left to right.

Procedural lighting (proceduralIBL), current code:

Procedural lighting, corrected code. Note the more linear trend in brightness from left to right.

Local Sandcastle for testing