Make MONAI robust to non-default meta dict names

[atbenmurray]

This PR adds a field to the meta dict indicating which tensor it belongs to, and a method get_meta_dict_key to find the meta_dict when it is present in a dictionary.

I have addressed many of the obvious places where there might be issues if the default meta_dict extension is not used but there are likely more that I need to find.

Description

A few sentences describing the changes proposed in this pull request.

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[einsyang723]

@atbenmurray ,
Hi, since the method you proposed involves looping through the data, resulting in O(n) time complexity. We would like to ask if it’s possible to add a dictionary to make the lookup more intuitive and faster, achieving O(1) time complexity.

key_to_meta_key_map[key] = meta_key
...
d["key_meta_dict_map"] = key_to_meta_key_map

Then our d would like:

--- image{}
|
--- image_meta_dict{}
|
--- lebel{}
|
--- lebel_meta_dict{}
|
--- key_meta_dict_map{"image": "image_meta_dict", "lebel": "lebel_meta_dict"}

with @slicepaste , @IamTingTing

[IamTingTing]

Is this part of the code to prevent meta_keys from being modified or deleted?
However, if a meta_key were deleted, the get_meta_dict_name() function would not be able to find the corresponding meta_key.
As for the possibility of meta_keys being modified, we have not found any function that could alter it.
Therefore, the condition here might be overlapping with the original code.
Could you kindly share the reason for adding it?

with @einsyang723 and @slicepaste