solve_multivar does not work with gensym-d names

[AayushSabharwal]

MWE:

@variables y z
x = Symbolics.variable(gensym(:x))
symbolic_solve([1 - x - y^2, z - x - y], [x, y, z])

throws:

ERROR: DomainError with Lex{Num}(Num[var"##x#305", y, z, _T], false):
The given monomial ordering is inconsistent with the input.
The variable var"##x#305" does not seem to belong to the ring: DynamicPolynomials.Variable{DynamicPolynomials.Commutative{DynamicPolynomials.CreationOrder}, MultivariatePolynomials.Graded{MultivariatePolynomials.LexOrder}}[##x#305, y, z, _T].

Variable mapping: Dict{DynamicPolynomials.Variable{DynamicPolynomials.Commutative{DynamicPolynomials.CreationOrder}, MultivariatePolynomials.Graded{MultivariatePolynomials.LexOrder}}, Int64}(##x#305 => 1, y => 2, z => 3, _T => 4)
Ordering: Lex{Num}(Num[var"##x#305", y, z, _T], false)
Stacktrace:
  [1] __throw_monomial_ordering_inconsistent(msg::String, var_to_index::Dict{…}, ord::Lex{…})
    @ Groebner ~/.julia/packages/Groebner/5Ez16/src/monomials/internal_orderings.jl:14
  [2] check_ordering_consistency(var_to_index::Dict{…}, ordering::Lex{…}, ring_vars::Vector{…}, ordering_vars::Vector{…}; part_of_a_product::Bool)
    @ Groebner ~/.julia/packages/Groebner/5Ez16/src/monomials/internal_orderings.jl:127
  [3] check_ordering_consistency
    @ ~/.julia/packages/Groebner/5Ez16/src/monomials/internal_orderings.jl:101 [inlined]
  [4] io_convert_to_internal_monomial_ordering(var_to_index::Dict{…}, ordering::Lex{…}; part_of_a_product::Bool)
    @ Groebner ~/.julia/packages/Groebner/5Ez16/src/monomials/internal_orderings.jl:159
  [5] io_convert_to_internal_monomial_ordering
    @ ~/.julia/packages/Groebner/5Ez16/src/monomials/internal_orderings.jl:153 [inlined]
  [6] io_set_monomial_ordering!(ring::Groebner.PolyRing{…}, var_to_index::Dict{…}, monoms::Vector{…}, coeffs::Vector{…}, params::Groebner.AlgorithmParameters{…})
    @ Groebner ~/.julia/packages/Groebner/5Ez16/src/input_output/input_output.jl:361
  [7] _groebner1(ctx::Groebner.Context, polynomials::Vector{…}, kws::Groebner.KeywordArguments{…}, representation::Groebner.PolynomialRepresentation)
    @ Groebner ~/.julia/packages/Groebner/5Ez16/src/groebner/groebner.jl:43
  [8] _groebner0(polynomials::Vector{DynamicPolynomials.Polynomial{…}}, kws::Groebner.KeywordArguments{Lex{…}})
    @ Groebner ~/.julia/packages/Groebner/5Ez16/src/groebner/groebner.jl:16
  [9] groebner(polynomials::Vector{DynamicPolynomials.Polynomial{…}}; options::@Kwargs{ordering::Lex{…}})
    @ Groebner ~/.julia/packages/Groebner/5Ez16/src/interface.jl:130
 [10] groebner_basis(polynomials::Vector{Num}; kwargs::@Kwargs{ordering::Lex{Num}})
    @ SymbolicsGroebnerExt ~/Julia/SciML/Symbolics.jl/ext/SymbolicsGroebnerExt.jl:38
 [11] solve_zerodim(eqs::Vector{Num}, vars::Vector{Num}; dropmultiplicity::Bool, warns::Bool)
    @ SymbolicsGroebnerExt ~/Julia/SciML/Symbolics.jl/ext/SymbolicsGroebnerExt.jl:202
 [12] solve_zerodim
    @ ~/Julia/SciML/Symbolics.jl/ext/SymbolicsGroebnerExt.jl:167 [inlined]
 [13] solve_multivar(eqs::Vector{Num}, vars::Vector{Num}; dropmultiplicity::Bool, warns::Bool)
    @ SymbolicsGroebnerExt ~/Julia/SciML/Symbolics.jl/ext/SymbolicsGroebnerExt.jl:304
 [14] solve_multivar
    @ ~/Julia/SciML/Symbolics.jl/ext/SymbolicsGroebnerExt.jl:303 [inlined]
 [15] symbolic_solve(expr::Vector{Num}, x::Vector{Num}; dropmultiplicity::Bool, warns::Bool)
    @ Symbolics ~/Julia/SciML/Symbolics.jl/src/solver/main.jl:204
 [16] symbolic_solve(expr::Vector{Num}, x::Vector{Num})
    @ Symbolics ~/Julia/SciML/Symbolics.jl/src/solver/main.jl:145
 [17] top-level scope
    @ REPL[23]:1