`similar` does not return a mutable container in the presence of `missing`

```
julia> x = @SVector [1,2,3,missing];

julia> y = similar(x)
4-element MVector{4, Union{Missing, Int64}} with indices SOneTo(4):
 #undef
 #undef
 #undef
 #undef

julia> y[1] = -1
ERROR: setindex!() with non-isbitstype eltype is not supported by StaticArrays. Consider using SizedArray.
```


I believe this is the cause of https://github.com/apache/arrow-julia/issues/486