Review Mozilla 1981499: Raise minSdkVersion to 26 (Android 8) for Fenix and Focus

🔍 Bugzilla Audit

Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1981499

Description

I don't think it's a very big deal for our code, but we'll have to update our docs.

This applies from Firefox 144 (16.0a1).

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