Fix overlap integrals for complex beams

[chrisbrahms]

This delightful little feature cost me several hours today: when doting two vectors containing complex values, the first is automatically conjugated:

help?> dot
search: dot @__dot__ stdout DEPOT_PATH adjoint fieldcount codepoint fieldoffset isdisjoint denominator modifyproperty! StridedVecOrMat DenseVecOrMat redirect_stdout DimensionMismatch

  dot(x, y)
  x ⋅ y

  Compute the dot product between two vectors. For complex vectors, the first vector is conjugated.

This PR removes additional manual conjugates to fix overlap integrals for beams which evaluate to complex-valued vectors (e.g. diverging Gaussian beams using Fields.gauss_beam). It also splits the integrals into real and imaginary parts to allow for potentially complex overlap integral values (ie a phase between the mode and the beam).

[jtravs]

LGTM, but see minor comments.