Hiding the favicon view when favicon is nil

[tomasstrba]

Task/Issue URL: https://app.asana.com/0/1199178362774117/1200960449542470/f

Description:
It is hard to navigate between tabs when a website has no favicon.

Steps to test this PR:

1. Please make sure the browser replaces favicon view with title when no favicon is provided. Especially when tabs are shrunk to their smallest size

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Internal references:

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[brindy]

This is looking good, but can we fix this bug as part of this? Testing this was problematic otherwise.

1. Open a new tab
2. Paste in https://www.bbc.co.uk
3. Then paste in https://www.synergylabs.org/yuvraj/pubs.html

Expected: No Favicon
Actual: No Favicon ✅

1. Open a new tab and paste in https://www.synergylabs.org/yuvraj/pubs.html

Expected: No Favicon
Actual: DDG Favicon 😭

Edit: Looks like updateFavicon never gets called when loading that URL which has no Favicon from a new tab
Edit: Setting favicon to nil in Tab.update(url:userEntered) when the content is homepage seems to fix it, but you might have a better solution.

    func update(url: URL?, userEntered: Bool = true) {
        if content == .homepage {
            favicon = nil
        }

        self.content = url == .homePage ? .homepage : .url(url ?? .blankPage)

        // This function is called when the user has manually typed in a new address, which should reset the login detection flow.
        userEnteredUrl = userEntered
     }

[tomasstrba]

@brindy, thanks for you review! Agree the bug is annoying, unfortunately favicons are going to be completely reimplemented soon - Fixing favicons - (my next TP). Do you think we could land this fix of the view layer?

[brindy]

LGTM!