Slow creation of CAs

It seems the slow (as per v0.50 release notes) kwargs constructor is being used for all CA creation and not just for the CA(...; x=y) syntax.

I'm not sure if this was the result of a recent change or if it has always been like this.

julia> @btime ComponentArray(a=5, b=[1, 2])
  23.316 μs (45 allocations: 2.14 KiB)
ComponentVector{Int64}(a = 5, b = [1, 2])

julia> @code_warntype ComponentArray(a=5, b=[1, 2])
Variables
  #unused#::Core.Compiler.Const(Core.var"#Type##kw"(), false)
  @_2::NamedTuple{(:a, :b),Tuple{Int64,Array{Int64,1}}}
  @_3::Type{ComponentArray}
  kwargs...::Base.Iterators.Pairs{Symbol,Any,Tuple{Symbol,Symbol},NamedTuple{(:a, :b),Tuple{Int64,Array{Int64,1}}}}

Body::Any
1 ─      (kwargs... = Base.pairs(@_2))
│   %2 = ComponentArrays.:(var"#ComponentArray#13")(kwargs..., @_3)::Any
└──      return %2

Start by tracing the ComponentArray constructor dispatch used by the named-argument example, then compare it with the kwargs path using the provided @btime and @code_warntype commands. Done means determining whether ordinary CA creation is incorrectly using the slow kwargs constructor and demonstrating the resulting performance difference.