Refactor: Cache DataTransferManager and items to share

[seer-by-sentry]

Resolved / Related Issues

To prevent extra work, all changes to the Files codebase must link to an approved issue marked as Ready to build. Please insert the issue number following the hashtag with the issue number that this Pull Request resolves.

• Closes FILES-APP-45M

Steps used to test these changes

Stability is a top priority for Files and all changes are required to go through testing before being merged into the repo. Please include a list of steps that you used to test this PR.

1. Reproduce the original issue that caused the NullReferenceException related to WinRT object garbage collection during share operations.
2. Verify that caching the DataTransferManager instance and the items to share prevents the NullReferenceException.
3. Ensure that share operations function correctly after the changes.
4. Run the application with the fix and monitor for any new exceptions or crashes related to share operations.
5. Test share operations with different file types and sizes.
6. Test share operations from different locations within the application.