RFR: 8279315: Add Git support to update_copyright_year.sh script

[Dmitry Kulikov]

Modified the `make/scripts/update_copyright_year.sh` script to support Git as well as Mercurial, as per [JDK-8279315](https://bugs.openjdk.java.net/browse/JDK-8279315). Also added the ability to specify company name as a command line argument instead of being hard-coded into the script.

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Commit messages:
 - 8279315: Add Git support to update_copyright_year.sh script

Changes: https://git.openjdk.java.net/jdk/pull/7027/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7027&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279315
  Stats: 56 lines in 1 file changed: 37 ins; 4 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7027.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7027/head:pull/7027

PR: https://git.openjdk.java.net/jdk/pull/7027