Preserve eltype in converting `Symmetric` to `Matrix` (#52738)
This allows cases where the `eltype` differs from that of the parent:
```julia
julia> M = [UpperTriangular([1 2; 3 4]) for i in 1:2, j in 1:2]
2×2 Matrix{UpperTriangular{Int64, Matrix{Int64}}}:
[1 2; 0 4] [1 2; 0 4]
[1 2; 0 4] [1 2; 0 4]
julia> H = Hermitian(M)
2×2 Hermitian{AbstractMatrix, Matrix{UpperTriangular{Int64, Matrix{Int64}}}}:
[1 2; 2 4] [1 2; 0 4]
[1 0; 2 4] [1 2; 2 4]
julia> Array(H)
2×2 Matrix{AbstractMatrix}:
[1 2; 2 4] [1 2; 0 4]
[1 0; 2 4] [1 2; 2 4]
```
This conversion throws an error at present on master.
