[m-rev.] for review: clean up bitmap.m

[Julien Fischer]

On Sat, 1 Jan 2022, Zoltan Somogyi wrote:

> Eliminate overuse of ^s in library/bitmap.m.
> 
> library/bitmap.m:
>     Replace all uses of field access notation for things that are not
>     structure fields with getter functions and setter predicates.
>     Add the getter functions and setter predicates where they did not
>     exist before. Unlike the old "field :=" functions, the new setter
>     predicates lend themselves to state variable notation.
>
>     Replace nested applications of functions with sequences of calls
>     (usually a get/modify/set sequence) that is easier to read and
>     understand, partly because it gives meaningful names to the
>     intermediate values.
>
>     Where an operation was available as both a function and a predicate,
>     implement the function version in terms of the predicate version,
>     as is our convention in the rest of the Mercury implementation,
>     instead of vice versa.
>
>     In a few cases, where implementing the function in terms of the predicate
>     could lead to misleading exceptions (that refer to the name of the
>     predicate, not the function, even when the user called the function),
>     have two copies of the implementation that differ only in the
>     text of the exception(s) being thrown.
> 
> NEWS:
>     Document the added exported functions and predicates.
> 
> tests/hard_coded/bitmap_empty.m:
>     Replace io.write/io.nl sequences with io.write_line, including
>     one case where the io.nl was missing :-(
>
>     Fix misleading indentation.

That's fine.

Julien.