[Light Switch] Enable theme switching with schedule

[Jaylyn-Barbee]

Summary of the Pull Request

This PR introduces behavior to allow users to attach a theme file to both light and dark mode which will switch when the color mode changes.

PR Checklist

• [x] Closes: #42413
• [x] Communication: I've discussed this with core contributors already. If the work hasn't been agreed, this work might be rejected
• [x] Localization: All end-user-facing strings can be localized
• [ ] Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

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Notes

1. How do we tell people that their theme files are saved at C:\Users\username\AppData\Local\Microsoft\Windows\Themes, the file picker just opens to a default location.
2. Double check that the theme is applying both on schedule and with the use of the shortcut.
3. On back burner for now until we can figure out a better solution for the Settings app issue.

[karlingen]

Thank you for your work on this! What's left to get this PR published?

[Jaylyn-Barbee]

@karlingen

As it stands, the code in this PR will invoke the theme file just with the side effect of opening the settings app. I am struggling to find a solution in C++ to invoke this file without the settings app opening. This is the only thing blocking this PR besides polishing things up and testing.