Support VT("name") where VT::Type{<:Variable}

[timholy]

Rather than creating a variable with Variable(name, V, M),
sometimes it's easier to create one with Variable{V,M}(name).
This allows one to create a new variable from an old one with
typeof(oldvar)(newname).

[blegat]

Indeed, that's a convenient syntax.
I usually use the following: https://juliaalgebra.github.io/MultivariatePolynomials.jl/dev/types/#MultivariatePolynomials.similar_variable
when I want my code to work with TypedPolynomials as well for which this won't work but code only meant for DynamicPolynoials, I can see this being useful

[timholy]

I just discovered similar_variable!

Since this is the first thing I thought of, perhaps for generic programming it could be added to TypedPolynomials too? In essence, have that constructor call similar_variable.

[blegat]

For TypedPolynomials, the type depends on the name so it would be weird to have Variable{:x}(Val{:y}) return Variable{:y}:

julia> typeof(x)
Variable{:x}

julia> typeof(similar_variable(x, Val{:y}))
Variable{:y}

[timholy]

Yeah, that would definitely be bad. I hadn't played enough with TypedPolynomials to realize what that would look like.