add `LinearAlgebra.inv` methods for `AbstractSymbolicOperator` subtypes

[Krastanov]

julia> inv(tCNOT)
X₁ ⟼ + XX
X₂ ⟼ + _X
Z₁ ⟼ + Z_
Z₂ ⟼ + ZZ

julia> inv(sCNOT(1,2))
ERROR: MethodError: no method matching inv(::sCNOT)

julia> inv(CliffordOperator(sCNOT))
X₁ ⟼ + XX
X₂ ⟼ + _X
Z₁ ⟼ + Z_
Z₂ ⟼ + ZZ