Drop combine_size

[N5N3]

This PR tries to perform combine_size during Broadcast.instantiate:

1. For broadcast, combine_axes will return a Tuple{Vararg{SOneTo}}, thus the output size has been static.
2. For broadcast!, the dest's axes is marked as static (if possible). If there's no size-1 dim in src. The current generated kernal will be called.

With this change, we can reduce the compile time for first broadcast by about 1/4:

julia> a = @SArray zeros(3,3)
3×3 SMatrix{3, 3, Float64, 9} with indices SOneTo(3)×SOneTo(3):
 0.0  0.0  0.0
 0.0  0.0  0.0
 0.0  0.0  0.0

julia> @time a .+ a;
  0.234903 seconds (452.90 k allocations: 24.654 MiB, 99.75% compilation time) #  on master: 0.308612 seconds (513.89 k allocations: 27.912 MiB, 99.87% compilation time)

[thchr]

Someone knowledgeable about the broadcasting machinery should review this probably - but I was reading this and figured I might as well add the few comments I had.

[mateuszbaran]

I've done some work with broadcasting before but I'm not quite familiar with certain parts of broadcasting touched in this PR.

[mateuszbaran]

I think this looks fine 👍 .

[mateuszbaran]

Could you bump patch version? I'd tag a new release.

[N5N3]

Could you bump patch version? I'd tag a new release.

Patch version was bumped in #1001. (master is 1.4.2 at present). I guess there's no need to bump again?

[mateuszbaran]

Yes, right, I didn't notice.

[judober]

I think this affects HybridArrays. See:
JuliaArrays/HybridArrays.jl#50