Do not trim protocol off of URLs ever

🔍 Bugzilla Audit

Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1902237

Description

In the 14.5 release URLs displayed in the url bar that started with http:// had this part trimmed away for display purposes. This does not happen for https:// schemes. This was controlled by the browser.urlbar.trimHttps preference, which is false.

With the upstream change, the browser.urlbar.trimHttps preference is ignored and overridden by browser.urlbar.scotchBonnet.enableOverride, which is true. As a result, https:// is trimmed, and http:// is not.

The major effect for us is .onion sites, which tend to be http://. As such, we should make an exception for .onion. Either:

1. Never trim the scheme for .onion addresses.
2. Only trim http:// for .onion addresses.

NOTE: I think the idea from upstream is that we should only trim the scheme that is assumed. I.e. if the user only types the address without a scheme, will they be taken to the http:// or the https:// site by default? For plain HTTP(S), it is the latter. I'm not sure for .onion, but it seems to be http:// when testing with pierov's onion site.

NOTE: Search for "trimHttps" for the relevant code.

/cc @donuts @morgan @pierov

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