Check mutation of elements from readonly map iterator

[fxamacker]

Updates #409

Projects using atree might unintentionally mutate elements returned by readonly iterators.

As always, mutation of elements from readonly iterators are not guaranteed to persist.

This PR returns error from mutation functions, and supports callback functions that allow projects using atree to log or debug such mutations with extra context, panic, etc.

If elements from readonly iterators are mutated:

• those changes are not guaranteed to persist.
• mutation functions of child containers return ReadOnlyIteratorElementMutationError.
• ReadOnlyMapIteratorMutationCallback are called (if provided and mutation occurs).

Two callback functions can be provided by using ReadOnlyIteratorWithMutationCallback.

func (m *OrderedMap) ReadOnlyIteratorWithMutationCallback(
	keyMutatinCallback ReadOnlyMapIteratorMutationCallback,
	valueMutationCallback ReadOnlyMapIteratorMutationCallback,
) (MapIterator, error) 

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• Targeted PR against main branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[turbolent]

Great work, thanks for adding this! I'll make the usage in Cadence more robust 👍