RFR: vcs: split unified and git raw diff parser

[Erik Helin]

Hi all,

please review this refactoring that splits the `UnifiedDiffParser` classes into the classes `UnifiedDiffParser` and
`GitRawParser`.

Thanks,
Erik

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Commit messages:
 - vcs: split unified and git raw diff parser

Changes: https://git.openjdk.java.net/skara/pull/876/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=876&range=00
  Stats: 761 lines in 10 files changed: 392 ins; 359 del; 10 mod
  Patch: https://git.openjdk.java.net/skara/pull/876.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/876/head:pull/876

PR: https://git.openjdk.java.net/skara/pull/876