RFR: Add CheckBuilder::from

[Erik Helin]

Hi all,

this small patch adds the method `CheckBuilder::from` that allows a `CheckBuilder` to be initialized to all the values from an existing `Check`, thereby enabling modifying a `Check` (while still preserving the old `Check`).

## Testing
- [x] `sh gradlew test` passes
- [x] Added one new unit test

Thanks,
Erik

----------------

Commits:
 - b97049ef: Add CheckBuilder::from

Changes: https://git.openjdk.java.net/skara/pull/175/files
 Webrev: https://webrevs.openjdk.java.net/skara/175/webrev.00
  Stats: 130 lines in 3 files changed: 130 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/175.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/175/head:pull/175

PR: https://git.openjdk.java.net/skara/pull/175