Bug with complicated function dependencies

[m0ose]

There was a bug when someone added a bunch of interdependent functions. I think it had to do with the order that they were declared in the shader.
Here is a fix and a test for #727.

[fuzzie360]

This looks like a real fix for #727 and the 16-function dependency test is appreciated. One concern before we merge: the reworked traceFunctionCalls recurses into callees unconditionally, so a cyclic call graph (a→b→a) that previously terminated would now recurse infinitely — hanging instead of erroring. Cycles are invalid for GLSL anyway, but a guard (e.g. a currently-tracing set that throws a descriptive error on re-entry) would make this safe. Would you be up for adding that? If not, say the word and we will take it over the finish line — CI now validates every PR automatically.