Allow bitarray to handle shifts by a negative value

[dbeach24]

Fix for #16706.
This allows left/right shifting a bitarray by a negative value.

[dbeach24]

@eschnett Could you please verify that this does what you wanted?

[dbeach24]

Is this merge-worthy?

[tkelman]

LGTM, though the merge commit should be squashed out (at merge time if needed)

[rfourquet]

Maybe, for completeness, add a test for b1 >> -m ?

[dbeach24]

Done

[rfourquet]

LGTM too.

[rfourquet]

Also while you are at it, you could update the docs for shift operations (e.g. the doc for >> implicitly assumes that the LHS is an integer type (with a sign)). Otherwise let's open a doc issue for that.

[dbeach24]

@rfourquet Not clear on how to update the docs. The docstrings for the shift operators are found in base/operators.jl, where the methods are defined for integer types. I don't want to change the signature of these functions (since they are specific to Integer).

Can you clarify what I'm supposed to do here?

[rfourquet]

I think it would be enough to attach additional docstrings to the shift methods acting on bitarrays.

[kshyatt]

I'm bumping this - can we merge this as-is and deal with the docs later? Alternatively, can someone guide @dbeach24 through the process of adding the docstrings?

[rfourquet]

I think it can, but would be nice to at least open a doc issue.

[tkelman]

replaced by #19760