Improving map management

[viktormalik]

I have prepared a large series with major refactoring of map management in bpftrace. To simplify reviewing, I'm going to post it in as small parts as possible but I realized that it would be good to provide an overview of all changes in advance.

The current plan is as follows:

• Use unique names for stackid maps #2910
• Introduce BpfBytecode class #2912
• Emit maps in libbpf style (with BTF) #2941. Thanks to this, part of the map information (type, key/value size, max entries) will be stored inside the generated ELF.
• Move map management to BpfBytecode #2988
• Delete MapManager, IMap, Map, and FakeMap classes.

Overall, this simplifies the code (we especially get rid of the ugly IMap/Map constructors) and also is the next step towards libbpf-based loading and attachment of programs. We should be eventually able to let libbpf auto-generate the maps for us.

[viktormalik]

All items are done, closing.