RFR: 8332257: Shenandoah: Move evacuation methods to implementation file

[William Kemper]

This refactoring moves a large, complex function out of an include header. This improves build times and facilitates changes in the generational mode branch.

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Commit messages:
 - Do not inline evacuate_object

Changes: https://git.openjdk.org/jdk/pull/19240/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19240&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332257
  Stats: 155 lines in 3 files changed: 77 ins; 77 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19240.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19240/head:pull/19240

PR: https://git.openjdk.org/jdk/pull/19240