RFR: 8357920: Add .rej and .orig to .gitignore

[Magnus Ihse Bursie]

The file types .rej and .orig are often created by diff tools. Adding them to .gitignore will help people from mistakenly committing these files.

See https://github.com/openjdk/jdk/pull/25306#discussion_r2102407122 for an example of where this happened.

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Commit messages:
 - 8357920: Add .rej and .orig to .gitignore

Changes: https://git.openjdk.org/jdk/pull/25474/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25474&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357920
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25474.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25474/head:pull/25474

PR: https://git.openjdk.org/jdk/pull/25474