missing `similar` method for `PseudoBlockArray` (`mapslices` unusable)

julia> using BlockArrays

julia> b = mortar([rand(5,5) for i=1:2, j=1:2]);

julia> mapslices(identity, b[1:5,:]; dims=1)
ERROR: MethodError: no method matching similar(::Vector{Float64}, ::Type{Float64}, ::Tuple{UnitRange{Int64}, UnitRange{Int64}})
Closest candidates are:
  similar(::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{N}}, ::Type{ElType}, ::Any) where {N, ElType} at C:\Users\sternlab\AppData\Local\Programs\Julia-1.7.2\share\julia\base\broadcast.jl:212
  similar(::Base.Broadcast.Broadcasted{Base.Broadcast.ArrayConflict}, ::Type{ElType}, ::Any) where ElType at C:\Users\sternlab\AppData\Local\Programs\Julia-1.7.2\share\julia\base\broadcast.jl:217
  similar(::ArrayLayouts.MulAdd{<:Any, <:ArrayLayouts.DualLayout, ArrayLayouts.ZerosLayout}, ::Type{T}, ::Any) where T at C:\Users\sternlab\.julia\packages\ArrayLayouts\nCtQC\src\muladd.jl:414
  ...
Stacktrace:
 [1] similar(a::Vector{Float64}, dims::Tuple{UnitRange{Int64}, UnitRange{Int64}})
   @ Base .\abstractarray.jl:783
 [2] mapslices(f::typeof(identity), A::PseudoBlockMatrix{Float64, Matrix{Float64}, Tuple{Base.OneTo{Int64}, BlockedUnitRange{Vector{Int64}}}}; dims::Int64)
   @ Base .\abstractarray.jl:2795
 [3] top-level scope
   @ REPL[5]:1

This is a regression introduced between 0.16.17 and 0.16.18

Reproduce the Julia 1.7 example using BlockArrays and mapslices(identity, b[1:5,:]; dims=1), then inspect PseudoBlockArray's existing allocation and similar methods. Done means the reported mapslices call no longer raises the missing similar(::Vector, ...) MethodError and the regression is covered by an appropriate test.