safety-context-dialog: Minor UI tweaks

Use AdwPreferencesGroup in all sections

Also:

• Fixes an AdwPreferencesGroup being inside another AdwPreferencesGroup, which is wrong
• Don't set margins in the widgets. Use the margins provided by AdwPreferencesGroup to ensure consistent spacing between the sections

Use an info popover to explain about outdated SDKs

The a11y label doesn't work and the warning icon doesn't have a tooltip; there is only the red color change, but this isn't sufficient to explain why an outdated SDK is bad.

Add a title in the permissions section

Doing so, this section will be more clear about its meaning.

Remove unneeded placeholders