feat(vscode): publish release VSIX assets

[mshanemc]

Summary

• Add separate reusable workflows that publish every VSIX attached to a caller repository release to VS Code Marketplace or Open VSX.
• Share release download, recursive VSIX discovery, and prerelease detection in a composite action.
• Preserve the GitHub release pre-release state, skip duplicate marketplace versions, and support safe workflow-level dry runs.
• Document both release-asset publisher workflows.

Verification

• actionlint .github/workflows/vscode-publish-release-vsix.yml .github/workflows/openvsx-publish-release-vsix.yml
• YAML parsing and Prettier checks for the new action and workflows.
• Downloaded and inspected the 17 VSIX assets from forcedotcom/salesforcedx-vscode release v67.10.0; confirmed its stable release state and flat asset layout.
• Tested recursive nested VSIX discovery and both dry-run paths; neither invokes a publish CLI, and the Open VSX token is not logged.

What issues does this PR fix or reference?

No related issues or discussions.

[skip-validate-pr]