feat(tonemap): add GTTonemap

[mqhaji]

Adds support for GTTonemap (Gran Turismo)
takes float and float3 inputs
https://www.desmos.com/calculator/gslcdxvipg
http://cdn2.gran-turismo.com/data/www/pdi_publications/PracticalHDRandWCGinGTS.pdf

// Uchimura 2018, "Practical HDR and Wide Color Techniques in Gran Turismo SPORT"
// https://www.desmos.com/calculator/gslcdxvipg
// http://cdn2.gran-turismo.com/data/www/pdi_publications/PracticalHDRandWCGinGTS.pdf
#define GTTONEMAP_GENERATOR(T)                \
  T GTTonemap(T x,                            \
              float P = 1.f,                  \
              float a = 1.f,                  \
              float m = 0.22f,                \
              float l = 0.4f,                 \
              float c = 1.33f,                \
              float b = 0.f) {                \
    float l0 = ((P - m) * l) / a;             \
    float L0 = m - (m / a);                   \
    float L1 = m + (1.0f - m) / a;            \
                                              \
    T S0 = m + l0;                            \
    T S1 = m + a * l0;                        \
    T C2 = (a * P) / (P - S1);                \
    T CP = -C2 / P;                           \
                                              \
    T w0 = 1.0f - smoothstep(0.0f, m, x);     \
    T w2 = step(m + l0, x);                   \
    T w1 = 1.0f - w0 - w2;                    \
                                              \
    T T_ = m * pow(x / m, c) + b;             \
    T S_ = P - (P - S1) * exp(CP * (x - S0)); \
    T L_ = m + a * (x - m);                   \
                                              \
    return T_ * w0 + L_ * w1 + S_ * w2;       \
  }

GTTONEMAP_GENERATOR(float)
GTTONEMAP_GENERATOR(float3)
#undef GTTONEMAP_GENERATOR