GH-3589: Add SPDX-License-Identifer; ensure consistent text format

[afs]

GitHub issue resolved #3589

Header changes for Java and POM files.

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• Key commit messages start with the issue number (GH-xxxx)

By submitting this pull request, I acknowledge that I am making a contribution to the Apache Software Foundation under the terms and conditions of the Contributor's Agreement.

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See the Apache Jena "Contributing" guide.

[rvesse]

Well that's one way to massively boost your changed lines stat 😉

Change makes sense as already discussed on #3695 and mailing lists, reviewed a sample of files and new headers look good to me

[afs]

"Contributions per week to main, line counts have been omitted because commit count exceeds 10,000."

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