Make `hvcat` for StaticArray and UniformScaling inputs produce a StaticArray

hcat and vcat seem to be specialized for StaticArray blocks, but hvcat does not seem to be specialized. Examples

julia> using StaticArrays

julia> A, B = @SMatrix(randn(2, 2)), @SMatrix(randn(2, 2));

julia> [A B] # fine
2×4 SMatrix{2, 4, Float64, 8} with indices SOneTo(2)×SOneTo(4):
  1.26449    0.426149  -1.15767    0.218855
 -0.816403  -0.241287  -0.663465  -0.367645

julia> [A; B] # fine
4×2 SMatrix{4, 2, Float64, 8} with indices SOneTo(4)×SOneTo(2):
  1.26449    0.426149
 -0.816403  -0.241287
 -1.15767    0.218855
 -0.663465  -0.367645

julia> [A B; A B] # Matrix
4×4 Matrix{Float64}:
  1.26449    0.426149  -1.15767    0.218855
 -0.816403  -0.241287  -0.663465  -0.367645
  1.26449    0.426149  -1.15767    0.218855
 -0.816403  -0.241287  -0.663465  -0.367645

julia> [A B; I] # Matrix
6×4 Matrix{Float64}:
  1.26449    0.426149  -1.15767    0.218855
 -0.816403  -0.241287  -0.663465  -0.367645
  1.0        0.0        0.0        0.0
  0.0        1.0        0.0        0.0
  0.0        0.0        1.0        0.0
  0.0        0.0        0.0        1.0

Start by locating the hcat and vcat specializations for StaticArray blocks and the corresponding hvcat entry point, then reproduce the examples in the issue. Done means hvcat cases involving StaticArray blocks and UniformScaling inputs produce a StaticArray rather than a Matrix, with coverage for the shown combinations.