Methods for multiplication OneHotMatrix * AbstractMatrix

[mcabbott]

Continuation of #56 , allows multiplication with OneHotMatrix on the left. All of these cases work:

julia> using OneHotArrays, JLArrays, LinearAlgebra, Test

julia> for op1 in (identity, adjoint), op2 in (identity, adjoint), order in (identity, reverse)
         m1, m2 = order([rand(3,3), onehotbatch([1,2,2], 1:3)])
         A, B = op1(m1), op2(m2)
         C = A * B
         try
           jlC = jl(A) * jl(B)
           @test Array(jlC) ≈ C
         catch e
           @error "A*B failed" typeof(A) typeof(B)
         end
       end

julia> for op1 in (identity, adjoint), op2 in (identity, adjoint), order in (identity, reverse)
         m1, m2 = order([rand(3,3), onehotbatch([1,2,2], 1:3)])
         A, B = op1(m1), op2(m2)
         C = A * B
         try
           jlC = mul!(jl(similar(C)), jl(A), jl(B))
           @test Array(jlC) ≈ C
         catch e
           @error "mul!(C,A,B) failed" typeof(A) typeof(B)
         end    
       end

... but there are some ambiguities:

julia> ohm = onehotbatch([1,2,2], 1:3);

julia> ohm * ohm
ERROR: MethodError: *(::OneHotMatrix{UInt32, Vector{UInt32}}, ::OneHotMatrix{UInt32, Vector{UInt32}}) is ambiguous.

Candidates:
  *(A::OneHotMatrix, B::AbstractMatrix{<:Number})
    @ OneHotArrays ~/.julia/dev/OneHotArrays/src/linalg.jl:13
  *(A::AbstractMatrix, B::OneHotLike)
    @ OneHotArrays ~/.julia/dev/OneHotArrays/src/linalg.jl:1
  *(A::AbstractMatrix, B::Union{OneHotArray{var"#s29", 1, var"N+1", I}, Base.ReshapedArray{Bool, var"N+1", <:OneHotArray{var"#s29", <:Any, <:Any, I}}} where {var"#s29", var"N+1", I})
    @ OneHotArrays ~/.julia/dev/OneHotArrays/src/linalg.jl:7

Possible fix, define
  *(::OneHotMatrix, ::Union{Base.ReshapedArray{Bool, 2, <:OneHotArray{T, <:Any, <:Any, I}} where {T, I}, OneHotMatrix})

Needs tests. And perhaps a use case.

PR Checklist

• Tests are added
• Documentation, if applicable