gendwarfksyms: Expand structure types

gendwarfksyms: Expand structure types

Recursively expand DWARF structure types, i.e. structs, unions, and
enums. Also include relevant DWARF attributes in type strings to
encode structure layout, for example.

Example output with --dump-dies:

  subprogram (
    formal_parameter structure_type &str {
      member pointer_type {
        base_type u8 byte_size(1) encoding(7)
      } data_ptr data_member_location(0) ,
      member base_type usize byte_size(8) encoding(7) length data_member_location(8)
    } byte_size(16) alignment(8) msg
  )
  -> base_type void

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>