`safe_unwrap` does not work on Complex{Num}

[aplund]

The safe_unwrap function leaves complex defined variables wraped. This can lead to breakages if the terms are assumed to be unwraped. (e.g. the use of operation in the chain_flatten_array_variables function). Below is a simple test.

using Symbolics
using PDEBase

@variables r c::Complex

println(typeof(r))
println(typeof(PDEBase.safe_unwrap(r)))
println()
println(typeof(c))
println(typeof(PDEBase.safe_unwrap(c)))

The output I get is

Num
SymbolicUtils.BasicSymbolic{Real}

Complex{Num}
Complex{Num}

The unwrap function in Symbolics returns a ComplexTerm.

[aplund]

It would seem that safe_unwrap is mostly unnecessary. The current implementation of unwrap applies a catch-all method which is just the identity, the same as what happens with safe_unwrap.