[FEATURE] Support saving of lists and dicts in a formatted way, including other SavesProjectID or Asset instances

[rayzchen]

Is your feature request related to a problem? Please describe.
When saving a Scene, SavedAttributes can only be saved properly if they are one of the following types: str, int, float, SavesProjectID (including Asset), Vector, Quaternion, RGB, HSV. However, it is also useful to support saving lists or dicts of these types, which could even support nesting.

Describe the solution you'd like
Such a format would be similar to YAML, with a few differences: the list format would have a different prefix other than - , the dict keys would be any of the above types properly formatted (maybe apart from the floating-point classes since they would rarely match) and indents would be 4 spaces instead of 2.

Describe alternatives you've considered
Currently, the SavableStruct has a similar format but does not support nesting.

Additional context
This would make Button be able to save the kwargs argument in the Scene file.

[rayzchen]

Typechecking must be implemented somehow, which means the type given to SavedAttributes needs to be from typing.GenericAlias or something similar.

Undecided if recursive structures should be allowed.

The existing SavableStruct class decorator has promising code.