imag function for type Polynomial

[kpobrien]

Hi, is there a reason real and conj are defined for the type Polynomial but imag is not? If no reason not to, I can make a PR defining the analogous functions. As a MWE, the real, and conj calls work, but imag is not defined.

using Polynomials
p = Polynomial((6,3,3.0+1im))
real(p)
conj(p)
imag(p)

ERROR: MethodError: no method matching imag(::Polynomial{ComplexF64, :x})

Closest candidates are:
  imag(::Missing)
   @ Base missing.jl:101
  imag(::LinearAlgebra.UnitLowerTriangular)
   @ LinearAlgebra ~/.julia/juliaup/julia-1.10.5+0.x64.linux.gnu/share/julia/stdlib/v1.10/LinearAlgebra/src/triangular.jl:160
  imag(::LinearAlgebra.UnitUpperTriangular)
   @ LinearAlgebra ~/.julia/juliaup/julia-1.10.5+0.x64.linux.gnu/share/julia/stdlib/v1.10/LinearAlgebra/src/triangular.jl:161
  ...

Stacktrace:
 [1] top-level scope
   @ REPL[5]:1

Thanks!