feat: frame count since build

[0b5vr]

This PR implements frame_count_since_build.

I implemented this in 2023-12 and completely forgot about it. I implemented it for pathtracing stuff I guess??
Feel free to reject this since I even don't know why I implemented this.

Working example

pipeline.yaml

stages:
  - fs: "scene.frag"
    target: accumulatorTex

  - fs: "present.frag"

scene.frag

#version 140

out vec4 out_color;

uniform vec4 resolution;
uniform int frame_count_since_build;
uniform sampler2D accumulatorTex;

void main() {
    out_color = texelFetch(accumulatorTex, ivec2(gl_FragCoord.xy), 0);
    int i = int(gl_FragCoord.x / 16) + int(gl_FragCoord.y / 16) * int(resolution.x / 16);
    if (i == frame_count_since_build) {
        out_color += vec4(0.5);
    }
}

present.frag

#version 430

out vec4 out_color;
uniform sampler2D accumulatorTex;

void main() {
    out_color = texelFetch(accumulatorTex, ivec2(gl_FragCoord.xy), 0);
}

[slerpyyy]

Seems like a nice uniform to have since it's symmetrical with time_since_build

Thank you for the PR!