Provide more ammo accessors

[mugling]

• Implements ammo_data() and ammo_current() from #14799 excluding handling of magazines
• Deprecates get_curammo_id() which is trivially replaced by ammo_current()
• Refactors item::weight() to use new accessors plus simplify logic and astyle

Further PR's will extend usage of these accessors and ultimately deprecate get_curammo. When we then merge the magazine type all functions using these accessors will be aware of magazines.

[chaosvolt]

I'm not sure if that is a step towards ammo overlap (see .38 Special plus .357 Magnum, .410 shotshells plus .45 Colt, etc) or something with different applications.

[mugling]

No, its just the two accessor functions extracted from #14799. They are intended to replace get_curammo_id and eventually get_curammo.

I'm going to work sequentially through consumers of get_curammo and check there are no likely issues when magazines are added and then change them to use ammo_data. Each logical block of functionality can have it's own PR for ease of testing to ensure there are no regressions. Finally we then re-add the magazine code to ammo_data and we're good to go with #14799 or it's successor.

[chaosvolt]

That would be failure to read on my part, as the original post states that this is tied to the shift towards magazines, Doh. >.<