POC: make math functions support complex arguments via anytype

[expikr]

An illustrative proof of concept accompanying #19207

• removes the math.complex namespace
• moves math.complex.arg/conj/proj to math.arg/conj/proj
• makes various math.* functions accept both real arguments as well as structs which contain re and im fields
• add math.ln that takes real or complex args (was a deprecated stub before, revived because math.log was already taken up by arbitrary-base logarithm)

closes #19207

[nektro]

the code doesnt pass zig fmt.