Create a new class that handles conversion worlds+embedded -> context data.
Create a derived class that uses static_server_data+pony instead.
There is also a not very efficient feature to deduplicate strings (may need perf testing).
By moving code around, we can simplify a lot of the world loading.
Where code lines were touched, some typing and some reformatting was added.
The back compat for GetDataPackage without games was finally dropped.
This was done as a cleanup because the refactoring touched those lines anyway.
Also reworked the per-context dicts and the RoomInfo to hopefully be more efficient
by ignoring unused games. (Generating the list of used games was required for the new
code anyway.)
Side effect of the MultiServer cache: we now load worlds lazily (but still all at once)
and don't modify the games package in place. If needed we create copies.
This almost gets us to the point where MultiServer doesn't need worlds - it still needs
them for the forbidden items.
There is a bonus optimization that deduplicates strings in name_groups that may have bad
performance and may need some perf testing if we run into issues.
