[Word/Excel] (keyboard shortcuts) Document backward compatibility support in the unified manifest

[samantharamon]

Documents how to create custom shortcut and localization files for backward compatibility in the unified manifest.

To the reviewer: This PR will be merged once the schema reference docs are updated. The PR doesn't remove preview language from the article. Let me know if we need to do so in this PR.

[learn-build-service-prod]

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[Copilot]

Pull Request Overview

This PR updates the documentation for custom keyboard shortcuts in Office Add-ins to detail the backward compatibility support in the unified manifest.

• The metadata date has been updated.
• The examples have been updated to remove add-in specific text in display names and include improved JSON examples for shortcuts and localization.
• New sections and note blocks have been added to explain how to support backward compatibility when publishing to AppSource.

[learn-build-service-prod]

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Learn Build status updates of commit 99f5f53:

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• [Error: CannotMergeCommit] Cannot merge commit 99f5f539c6f96754e93787e9960a684f25f7b460 in branch samramon-keyboard-shortcut-update of repository https://github.com/OfficeDev/office-js-docs-pr into branch main (commit a40f558f5dc3083eb5dfba6a4406cca154256e44). Please follow this documentation: https://help.github.com/articles/resolving-a-merge-conflict-using-the-command-line/ to use git.exe to resolve you content conflicts locally and then push to remote.

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[learn-build-service-prod]

Learn Build status updates of commit c1dc5c1:

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