Add Fx132 support for Notification.silent

[chrisdavidmills]

Summary

Firefox 132 supports the Notification.silent property.

This PR adds Fx support to that data point.

See the shipping bug at https://bugzilla.mozilla.org/show_bug.cgi?id=1809028

Test results and supporting details

I wrote a quick test case to test the property: see https://silent-notifications-test.glitch.me/.

I found the results somewhat inconclusive:

• In Firefox Nightly 133, the system notification fires and n.silent returns true.
• In Firefox beta 132, the system notification doesn't fire, but n.silent returns true (it supports the property).
• In Firefox release 131, the system notification doesn't fire, and n.silent returns undefined (it doesn't support the property).
• In the last couple of versions of Chrome and Safari, it all works just fine (same as Fx133).

This suggests that Fx 132 does support it, but there is something going on with the actual notification firing. Is it buggy, or did I do something wrong with the permissions code? I will ask the Fx devs to look at it.

Related issues

Docs issue: mdn/content#36119