Generalize broadcasting to StaticMatrixLike

[devmotion]

Currently, broadcasting with StaticMatrixLike-types does not always return SMatrix results:

julia> using StaticArrays, LinearAlgebra

julia> Symmetric(@SMatrix [1 2; 3 4]) .+ 1
2×2 Matrix{Int64}:
 2  3
 3  5

julia> Symmetric(@SMatrix [1 2; 3 4]) .+ @SVector [5, 6]
2×2 Matrix{Int64}:
 6   7
 8  10

julia> Symmetric(@SMatrix [1 2; 3 4]) .+ @SMatrix [5 6; 7 8]
2×2 SizedMatrix{2, 2, Int64, 2, Matrix{Int64}} with indices SOneTo(2)×SOneTo(2):
 6   8
 9  12

The PR fixes this by generalizing definitions of BroadcastStyle, isstatic, and axes to StaticMatrixLike:

julia> using StaticArrays, LinearAlgebra

julia> Symmetric(@SMatrix [1 2; 3 4]) .+ 1
2×2 SMatrix{2, 2, Int64, 4} with indices SOneTo(2)×SOneTo(2):
 2  3
 3  5

julia> Symmetric(@SMatrix [1 2; 3 4]) .+ @SVector [5, 6]
2×2 SMatrix{2, 2, Int64, 4} with indices SOneTo(2)×SOneTo(2):
 6   7
 8  10

julia> Symmetric(@SMatrix [1 2; 3 4]) .+ @SMatrix [5 6; 7 8]
2×2 SMatrix{2, 2, Int64, 4} with indices SOneTo(2)×SOneTo(2):
 6   8
 9  12

[mateuszbaran]

This looks reasonable. Could you just bump version to 1.7.0?

[devmotion]

Done 🙂