DYN-6103 Fix crash when undoing a group to group addition

[zeusongit]

Purpose

https://jira.autodesk.com/browse/DYN-6103

In case of 3 groups if we combine them it will add the other 2 groups to the main group.
The crash occurred was while removing more than 1 group from a group.

We maintain a List of nested groups(geometry) and a Dictionary of their GUIDs and index at which they are stored in the list.
While splitting a nested group, we run a loop of all the groups that are nested inside the main group, since in this case we have 2 groups inside the main group, the loop will run twice, in natural order. So it will remove the group at index 0 and then 1 ...etc.
Removing the group at index 0 will change the size of the List, and when the second iteration is run to remove the group at index 1, it throws the index out of bounds error, since the list has only 1 element at index 0 now.

To fix this I am running the loop backwards, so we always remove groups from the list starting from the end, and we will always find the current index in the list.

Also, edited the test to catch this error, which only tested with 2 groups previously.

Declarations

Check these if you believe they are true

• The codebase is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning and are documented in the API Changes document.
• This PR modifies some build requirements and the readme is updated
• This PR contains no files larger than 50 MB

Release Notes

• Fix crash when undoing a group to group addition

Reviewers

@DynamoDS/dynamo

[QilongTang]

One regression DynamoCoreWpfTests.JSONSerializationTests.SerializationTest("D:\jenkins\workspace\Dynamo\DynamoSelfServe\pullRequestValidation\Dynamo\test\core\annotationViewModelTests\groupsTestFile.dyn")

[zeusongit]

Will be closing this PR without merging, as changes in this PR were small enough and conflicting with the other PR (#14220).