Make broadcast return BitArray even if it cannot be inferred

[martinholters]

Thanks to #17623 broadcast returns BitArray instead of Array{Bool} if this can be decided based on inference:

julia> foo(x::Bool) = (x,"bla")[1] # can be inferred
foo (generic function with 1 method)

julia> foo.(trues(2))
2-element BitArray{1}:
 true
 true

julia> bar(x::Bool) = (x,"bla")[length([x])] # cannot be inferred
bar (generic function with 1 method)

julia> bar.(trues(2))
2-element Array{Bool,1}:
 true
 true

Reliance on inference should be avoided, so with this PR:

julia> bar.(trues(2))
2-element BitArray{1}:
 true
 true

[pabloferz]

I guess we could just check that f.([true, false]) == [true, "false"] here.

[martinholters]

Indeed. Update coming...

[martinholters]

Better be sure, so @nanosoldier runbenchmarks(ALL, vs = ":master")

[nanosoldier]

Your benchmark job has completed - possible performance regressions were detected. A full report can be found here. cc @jrevels

[martinholters]

The single benchmark regression is likely noise; broadcast is used so ubiquitously nowadays, a real regressions would likely have affected many more benchmarks.
Good to go?

[nalimilan]

BTW, shouldn't map also return a BitArray in the same cases as broadcast?