[Meta] Preview Theme `Next`

[KrooshalUX]

The following issues cover the scope for introducing and promoting the new "Next" theme

• (Look & Feel) New Light & Dark Mode Improvements  oui#895
• Switch default theme to "Next" from "V7" #4677
• Inform users of theme "Next" preview  #4676
• Updates to Advanced Settings for theme Next #4330
• Introduce appearance user controls  #4669

[KrooshalUX]

@joshuarrrr can you follow up here with the needed playground issues?

we should probably suppress the notification on playground since users will not be able to revert to v7

[DarshitChanpura]

@KrooshalUX Should we move this issue to 2.11?