FIx #2969 targetPath with collection nav props and add test.

[garethj-msft]

Issues

This pull request fixes #2969

Description

Fixes TargetPathHelper to correctly handle collection-valued navigation properties and provides a test.

Checklist (Uncheck if it is not completed)

• [x] Test cases added
• [ ] Build and test with one-click build and test script passed

Additional work necessary

If documentation update is needed, please add "Docs Needed" label to the issue and provide details about the required document change in the issue.

[garethj-msft]

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