added support for reduce(hcat, OneHotMatrix)

[pevnak]

[Please delete this text and describe your change here.
For bugfixes, please detail the bug and include a test case which your patch fixes.
If you are adding a new feature, please clearly describe the design, its rationale, the possible alternatives considered.
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This fixes a bug
#1596
by adding reduce(::typeof(hcat), Vector{TV}) where {TV<:OneHotLike}

PR Checklist

• [x ] Tests are added
• Entry in NEWS.md
• Documentation, if applicable
• API changes require approval from a committer (different from the author, if applicable)

[pevnak]

I have not noticed Matej fixed it here
#1595

[darsnack]

Actually the reduce(hcat, ...) case was removed from that PR before merging. The fix that we agreed upon was to define similar and setindex! for OneHotArrays (which should handle the reduce and other fast paths automatically).

There is an implementation of similar that I wrote in the comments for #1595 which will work. I never got around to setindex!, but a PR with those two changes would be appreciated.

[tantheta01]

@darsnack wanted to check if I could work on this issue or has a PR been created already?

[ToucheSir]

AFAIK nobody is working on it, but fair warning that the setindex! piece may be a little tricky!