This change moves almost everything in the `upb/` directory up one level, so
that for example `upb/upb/generated_code_support.h` becomes just
`upb/generated_code_support.h`. The only exceptions I made to this were that I
left `upb/cmake` and `upb/BUILD` where they are, mostly because that avoids
conflict with other files and the current locations seem reasonable for now.
The `python/` directory is a little bit of a challenge because we had to merge
the existing directory there with `upb/python/`. I made `upb/python/BUILD` into
the BUILD file for the merged directory, and it effectively loads the contents
of the other BUILD file via `python/build_targets.bzl`, but I plan to clean
this up soon.
PiperOrigin-RevId: 568651768
For LITE messages we append the type name to the data, avoiding an
indirection and a relocation.
For descriptor messages we mark them as such and have a secondary vtable. This
way we avoid having to put those pointers on each message ClassData. We save in
data size and relocations. If in the future we determine that the extra jump is
costly we can inline the relevant descriptor method pointers into `ClassData`.
PiperOrigin-RevId: 565775188
We do not want to repeatedly check `using_sso` when iterating over an array. Hence instead of using `Get(i) / Mutable(i)` from base class, we request a pointer to the underlying array (thus, reducing number of checks from N to 1).
Additionally, there is a loop with a `Delete` call - updated it to use `CommonHandler`, so that it reduces code bloat.
PiperOrigin-RevId: 565665669