GDExtension docs: Advise bindings to use uint64_t for bitfields

[Bromeon]

Closes- #88962, alongside related changes:

• Core: Change BitField internal value to uint64_t #94270
• Core: Change BitField internal value to uint64_t godot-cpp#1517

[Bromeon]

I wonder if @param p_is_bitfield is really the best place to mention this? Or should I move it up to the description part?

[dsnopek]

Thanks!

I wonder if @param p_is_bitfield is really the best place to mention this? Or should I move it up to the description part?

Personally, I think it'd be better up in the description, since it's better suited to longer text.

[Bromeon]

Updated.

[dsnopek]

Thanks! Looks good to me :-)

[akien-mga]

Thanks!