Multiple type signature possible problem

Related to issue #1978.

I scanned other GLSL implementations for includes that look like they would follow the same pattern as `smoothstep` in the issue above.

* `mx_dodge_color3.glsl` and `mx_dodge_color4.glsl` both include `mx_dodge_float.glsl`
* `mx_burn_color3.glsl` and `mx_burn_color4.glsl` both include `mx_burn_float.glsl`
* All the `splitlr` and `splittb` glsl source code files include `mx_aastep.glsl`

These nodes look like they might also exhibit the same issue as reported - though I have not confirmed this.

Start by reading issue #1978, then inspect the include relationships in mx_dodge_color3.glsl, mx_dodge_color4.glsl, mx_dodge_float.glsl, mx_burn_color3.glsl, mx_burn_color4.glsl, mx_burn_float.glsl, the splitlr and splittb source files, and mx_aastep.glsl. Done means confirming whether these patterns produce the same type-signature problem as smoothstep and identifying the affected files.

Written by the indexing model from the issue text.