shell_util: Move RegistryEntry methods out-of-line.
shell_util: Move RegistryEntry methods out-of-line.

This just moves the method definitions outside of the class declaration,
in preparation for a future refactoring. No code changes.

BUG=419972

Review URL: https://codereview.chromium.org/1472273003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#362011}

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