Add optimized findall(::AbstractArray{Bool}) method

[nalimilan]

Allocating result upfront is faster, but it is possible only when collection can be iterated twice.
This fixes a regression introduced when rewriting the generic method.

Fixes #25489.

@nanosoldier runbenchmarks(ALL, vs=":master")

[nalimilan]

Let's try again:
@nanosoldier runbenchmarks(ALL, vs=":master")

[nanosoldier]

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

[nalimilan]

Hmm, there are (probably spurious) improvements all over the place, but the relevant one (["find", "(\"Array{Bool,1}\", \"50-50\")]) is only 9% faster, with 22% less allocated memory, and others do not even show up. I wonder whether the deprecation of find may make the timings completely meaningless.

[ararslan]

The find stuff has been fixed in BaseBenchmarks (thanks Milan!!), so maybe this will be a little more representative.

@nanosoldier runbenchmarks(ALL, vs=":master")

[nanosoldier]

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

[nalimilan]

OK, with the new run ["find", "(\"Array{Bool,1}\", \"50-50\")] is three times faster and allocates half as much memory, which cancels the regression due to #24774. Local benchmarking shows that it's also the case with non-50/50 distributions, not sure why it's not visible (EDIT: that's because the benchmarks did not test them, see JuliaCI/BaseBenchmarks.jl#182). BitVector doesn't show up because it uses a specific method (I hadn't realized that).

[oscardssmith]

Does this method remove the need for specialized BitVector one?

[nalimilan]

No, I don't think so. The method this PR reintroduces used to exist already, both are useful.