Allow searching for subvectors of vectors in contains

[Keno]

I'd have expected the following to work:

julia> contains(UInt8[1, 2, 3], UInt8[2, 3])
ERROR: MethodError: no method matching contains(::Array{UInt8,1}, ::Array{UInt8,1})
Closest candidates are:
  contains(::Function, ::Any, ::Any) at reduce.jl:664

having the same meaning as it does for strings.

[nalimilan]

BTW, contains could be integrated to the find* family of functions. We could keep it as a convenience function, with a fallback to something like findfirst(sequence(needle), haystack) > 0.

[nalimilan]

See also #19250 and #18028. I think we should get rid of ismatch which is quite restrictive as it only works with regular expressions, and merge it with contains. This appears to be the consensus.

[JeffBezanson]

My only slight concern is that find* works with indices, and there could be cases where a sequence doesn't have indices or where it's more expensive to determine an index than to determine whether a match exists. But find* works for all current cases, so we can go ahead with switching to find*, and possibly add an issubseq that defaults to calling find(needle, haystack) > 0.