math_parser: evaluate variables in diag. functions

[andrei8l]

Summary

None

Purpose of change

Allow dialogue functions in math to evaluate their parameters from dialogue variables.

• Needed for math_parser: port skill_level functions to math #65465 to fully port the skill_level functions.

So something like

"condition": { "u_has_skill": { "skill": { "global_val": "myvar" }, "level": 5 } },

can be fully ported to

"condition": { "math": [ "u_skill(myvar)", ">=", "5" ] }

where myvar gets evaluated inside u_skill.

Describe the solution

Expand the math parser to include this use case

TODO:

• figure out validation: ez pz; I was overthinking it

Describe alternatives you've considered

Third party parser

Testing

New test units

Additional context

This includes a tiny bit of code from #65465 so that the tests work.

This will stay in draft until #65298 and #65465 get merged to spare myself some conflict resolution.

[andrei8l]

Thanks for merging!