[Bridges] restrict some bridges to acting on real-valued functions

[odow]

Follow-up to https://github.com/jump-dev/MathOptInterface.jl/pull/2451. It's too easy to run into obscure method errors because some bridges incorrectly accept Complex-valued functions.

• [x] https://github.com/jump-dev/MathOptInterface.jl/actions/runs/8594253802