Missing definition for ecs_meta_move

[sro5h]

Describe the bug
The definition of the function ecs_meta_move seems to be missing from flecs.c and meta.c. Thus usage of the function results in a linker error.

Expected behavior
No linker error.

Additional context
Should not really matter, but i am running Fedora 35 with gcc 11.3.1

[SanderMertens]

Fixed!

I made a few changes:

• renamed the function to ecs_meta_elem
• it can only be used with collections

Rationale: implementing an ecs_meta_move for structs could not be made more efficient (at least not without introducing additional data structures) than calling ecs_meta_next multiple times. This is because of nested structs, and the list of operations being "flattened": you can't easily jump over 3 members without knowing how many members those members have. Instead, the ecs_meta_member function provides an O(1) way to jump around a struct.

ecs_meta_move (now ecs_meta_elem) does make sense for collections, where "jump to the nth element" is a simple O(1) operation where the cursor just sets the index to the current element.