[aot] Add a generic set of AOT structs

[k-ye]

Related issue = #3334

I haven't really switched OpenGL or Vulkan to use these new AOT structs yet, but the migration should be very simple, e.g.,

auto ad = AotDataConverter::convert(aot_data_);
TextSerializer ts;
t2.serialize_to_json("aot_data", ad);
t2.print();

I've also added/removed/changed a few field names:

• ScalarArg
  • offset_in_bytes_in_args_buf --> offset_in_args_buf
• ogl::CompiledArrayArg --> aot::ArrayArg
  • shape_offset_in_bytes_in_args_buf --> shape_offset_in_args_buf
  • Added bind_index
• CompiledTaichiKernel
  • arg_count --> args_count
  • ret_count --> rets_count
  • args_buf_size --> args_buffer_size
  • ret_buf_size --> rets_buffer_size
  • Removed used.arr_arg_to_bind_idx

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[k-ye]

/format

[ailzhang]

Nice thanks!!
for the bind_idx, I agree it makes more sense to move from CompiledTaichiKernel to ArrayArg for opengl backend as well :D

[ailzhang]

IMHO it's fine to keep them as separate files?