1965485 - Preferences.addSetting should register dependent prefs if necessary

Status: NEW

(Firefox :: Settings UI, enhancement)

Description

[Mark Striemer [:mstriemer]]

When registering a Setting that depends on a pref with Preferences.addSetting({ id, pref }) it is required that the pref already be registered through Preferences.add() or Preferences.addAll() with its id and type. We can infer the type from the database however, so this should not be required

An example of detecting a pref's type from devtools: Searchfox

Acceptance criteria:

• When a setting is created with a pref key, that pref will be registered with an auto-detected type using Preferences.add({ id: pref, type: detectedType }) if it isn't already registered
• Testing that the auto-detection and registration works
• I believe this could cause problems if the pref doesn't have a default value, some settings specific testing that all auto-detected types have defaults could be wise (maybe just log + throw in the setup code when Cu.isInAutomation?)