deconstruct signalOptions config object, migrate settings

[meganrogge]

fix #213618

We added accessibility.signalOptions last iteration for easier discovery/grouping of these settings because they can otherwise get lost amongst the many accessibility.signals properties.

However, this had side effects:

• the delays property couldn't be easily adjusted in the settings UI due to the multiple nested objects. discussed this with @rzhao271 and it's a limitation of the settings UI.
• we want to track telemetry to determine if the experimental.delays are justified, but one cannot track data of a setting's property.
• searching in the settings UI doesn't factor in setting properties

This destructures that object and migrates the settings.

cc @hediet

[hediet]

Thank you!