generators: expose caller world to GeneratedFunctionStub (#48611)
Expose the demanded world to the GeneratedFunctionStub caller, for users
such as Cassette. If this argument is used, the user must return a
CodeInfo with the min/max world field set correctly.
Make the internal representation a tiny bit more compact also, removing
a little bit of unnecessary metadata.
Remove support for returning `body isa CodeInfo` via this wrapper, since
it is impossible to return a correct object via the
GeneratedFunctionStub since it strips off the world argument, which is
required for it to do so. This also removes support for not inferring
these fully (expand_early=false).
Also answer method lookup queries about the future correctly, by
refusing to answer them. This helps keeps execution correct as methods
get added to the system asynchronously.
This reverts "fix #25678: return matters for generated functions
(#40778)" (commit 92c84bf3865403355af463b5a1dee42bf7143592), since this
is no longer sensible to return here anyways, so it is no longer
permitted or supported by this macro.
Fixes various issues where we failed to specify the correct world.
