Version of `reshape` that preserves keys?

I'm not sure how helpful this would be generally, but a lot of ML APIs restrict input arrays to matrices. It'd be kind of nice if we could support at least a subset of the reshape behaviour such that axis keys are merged. For example:

julia> ka = KeyedArray(rand(4, 3, 2); time=1:4, obj=[:a, :b, :c], loc=[:x, :y])
3-dimensional KeyedArray(NamedDimsArray(...)) with keys:
↓   time ∈ 4-element UnitRange{Int64}
→   obj ∈ 3-element Vector{Symbol}
□   loc ∈ 2-element Vector{Symbol}
And data, 4×3×2 Array{Float64,3}:
[:, :, 1] ~ (:, :, :x):
      (:a)       (:b)        (:c)
 (1)   0.416197   0.327252    0.14608
 (2)   0.706717   0.0045184   0.055459
 (3)   0.487265   0.879403    0.121894
 (4)   0.156394   0.431853    0.0756667

[:, :, 2] ~ (:, :, :y):
      (:a)       (:b)       (:c)
 (1)   0.507      0.803645   0.411088
 (2)   0.92779    0.284998   0.418833
 (3)   0.137591   0.415834   0.194712
 (4)   0.785161   0.436941   0.996514

julia> reshape(ka, 4, :)
4×6 Array{Float64,2}:
 0.416197  0.327252   0.14608    0.507     0.803645  0.411088
 0.706717  0.0045184  0.055459   0.92779   0.284998  0.418833
 0.487265  0.879403   0.121894   0.137591  0.415834  0.194712
 0.156394  0.431853   0.0756667  0.785161  0.436941  0.996514

I feel like in these cases it would be nice if we could get something like:

julia> KeyedArray(reshape(ka, 4, :); time=1:4, obj_loc=[:a_x, :b_x, :c_x, :a_y, :b_y, :c_y])
2-dimensional KeyedArray(NamedDimsArray(...)) with keys:
↓   time ∈ 4-element UnitRange{Int64}
→   obj_loc ∈ 6-element Vector{Symbol}
And data, 4×6 Array{Float64,2}:
      (:a_x)     (:b_x)      (:c_x)      (:a_y)     (:b_y)     (:c_y)
 (1)   0.416197   0.327252    0.14608     0.507      0.803645   0.411088
 (2)   0.706717   0.0045184   0.055459    0.92779    0.284998   0.418833
 (3)   0.487265   0.879403    0.121894    0.137591   0.415834   0.194712
 (4)   0.156394   0.431853    0.0756667   0.785161   0.436941   0.996514

Either with reshape directly or at least with a separate, more restrictive, function call. If this seems like it could be useful for other folks I'm happy to open a PR with a suggested function name?

Start by reproducing the Julia KeyedArray and reshape(ka, 4, :) examples in the issue. Review the existing reshape and KeyedArray APIs, then determine and document the supported rule for merging axis keys. Done means the agreed behavior is implemented for the demonstrated case and covered by corresponding checks.