dpg typespec, use DEFAULT_VERSION as new version to compare Jars

[XiaofeiCao]

Description

For DPG typespec.
When folder is deleted and we don't do update_version, sdk version in pom.xml is DEFAULT_VERSION(1.0.0-beta.1) and so is the generated Jar.
https://dev.azure.com/azure-sdk/internal/_build/results?buildId=3934354&view=logs&j=a8a7a537-82b0-583c-7971-bac70b9822ca&t=37e3947b-3cfb-5d36-86ba-0e22bb7dbc33&l=883

Now in this case, we'll use DEFAULT_VERSION as current_version for Jar comparison.
Test in: test-repo-billy/azure-rest-api-specs#3398

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[weidongxu-microsoft]

/check-enforcer override