Define dot between UniformScaling and Matrix

[lkapelevich]

julia> using LinearAlgebra; U = UniformScaling(2); A = ones(2,2); dot(U, A)
ERROR: MethodError: no method matching iterate(::UniformScaling{Int64})
Closest candidates are:
  iterate(::Union{LinRange, StepRangeLen}) at range.jl:737
  iterate(::Union{LinRange, StepRangeLen}, ::Int64) at range.jl:737
  iterate(::T) where T<:Union{Base.KeySet{var"#s78", var"#s77"} where {var"#s78", var"#s77"<:Dict}, Base.ValueIterator{var"#s76"} where var"#s76"<:Dict} at dict.jl:693
  ...
Stacktrace:
 [1] dot(x::UniformScaling{Int64}, y::Matrix{Float64})
   @ LinearAlgebra C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.7\LinearAlgebra\src\generic.jl:876
 [2] top-level scope
   @ REPL[13]:1

I guess it would make sense for this use U.λ * tr(A)

[Keno]

I guess it would make sense for this use U.λ * tr(A)

That seems right given our usual generic definition for arrays (https://github.com/JuliaLang/julia/blob/ae3a3cc570a7c48603becb3a28edf1cc465884ce/stdlib/LinearAlgebra/src/generic.jl#L906) and our treatment of UnifromScaling as an indefinite-dimension array. Submit a PR?