Some code cleanup work

[daxian-dbw]

PR Summary

This is byproduct of the update notification work. Major changes:

• Move Utils.GetUserConfigurationDirectory to Platform.ConfigDirectory
• Unify the use of Platform.ConfigDirectory and Platform.CacheDirectory

PR Context

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[iSazonov]

xUnit test failed.

[ghost]

🎉v7.0.0-preview.5 has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes