Fix invalidation of soft container nested in a holster

[wwkk222208]

Summary

None

Purpose of change

There is a bug:
When picking up items, players can't put them into a soft container nested in a holster. (Players are not likely to do this in vallina DDA, but it will happen when using ‘lifting field’ of MindOverMatter). In addition, when the soft container is placed in a holster, the available capacity of the player will also be underestimated.
This PR is to solve it.

Describe the solution

1.Ignore regidity of nested pocket if current pocket is a holster.
2.If a pocket is a holster with an item, use the volume of contents when it is full as the pocket capacity. For non-container or rigid container, it is the volume of itself. For soft container it will add all of the remaining volume of soft valid pocket.

Describe alternatives you've considered

A soft holster nested in another one is not considered, which will lead to higher capacity showed on the UI. To obtain accurate results, a recursive function may be required. Since in the actual game this is very rare, from a performance perspective, it seems not worth it to do so.
Even if you do want to try that, it won't lead to worse results. Instead, if the result is lower than the actual, it will prevent you from picking up items normally.

Testing

Tested in game.

Additional context

Codes of nested container are really complicated!!

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[wwkk222208]

Thanks to SurFlurer for helping me complete this work！