Fix phone number serialization

[maximrytych-ms]

Fixed the logic of PhoneNumberIdentifier to always maintain the original phone number string whether it included the leading + sign or not.

[vcolin7]

Approved with a comment about the release date in the CHANGELOG.

[maximrytych-ms]

/azp run android - azure-communication-common - tests

[azure-pipelines]

No pipelines are associated with this pull request.

[AikoBB]

Pls add the bugfix info in the changelog:

### Bugs Fixed
- Fixed the logic of `PhoneNumberIdentifier` to always maintain the original phone number string whether it included the leading + sign or not.