Before this change, Aya supported only legacy BPF map definitions, which
are instances of the `bpf_map_def` struct and end up in the `maps` ELF
section. This change introduces BTF maps, with custom structs indicating
the metadata of the map, which end up in the `.maps` section.
Legacy maps are not supported by libbpf anymore and not even by the
kernel for newer types of maps like inode/task storage.
Add support of BTF maps in aya-ebpf under the `btf-maps` feature flag.
Usage of this feature requires emitting debug info for the eBPF crate
and passing the `--btf` flag to bpf-linker.
Added logic in expand function in both kprobe.rs and uprobe.rs for valid
macros. Now, kprobe & uprobe proc macros only accept ProbeContext, and
kretprobe & uretprobe only accept RetProbeContext.
Ref: #700