Allow spells to spawn items with their containers

[RedShakespeare]

Summary

SUMMARY: Features "Allow spells to spawn items with their containers"

Purpose of change

In current version if we want to use a spell to spawn something in liquid phase we have to prepare a container in advance or that item would fall onto ground. This pr is aimed to allow liquid spawned with containers.

Describe the solution

Add a "WITH_CONTAINER" flag for spells to spawn items with containers.

Describe alternatives you've considered

Let "effect_str" works as item_groups, not items (but that will lead to a thorough rewrite in current spells' definitions).

Testing

Not yet...but it should work technically.

Additional context

This could be used for future furnitures like sacrificial altar or something.

[KorGgenT]

please update the docs in flags.json and JSON_FLAGS.md

[RedShakespeare]

please update the docs in flags.json and JSON_FLAGS.md

Gotta do that immediately.
( But there's no flag about spells in JSON_FLAGS.md ... I'm not quite sure where I should add this in.

[KorGgenT]

oh i thought i put something in the markdown file. if i didn't then i guess i just did the json file as documentation

[RedShakespeare]

so it is. wwwwwwww
and....mission accomplished ( lol