regression: qt wizard should allow restoring from invalid bip39 seeds

[SomberNight]

This is a regression in the new wizard -- the old wizard allowed this.
Specifically, we should allow any string to be used as a "bip39" seed, and enable the "next" button, but only in the desktop qt gui. The errors shown by the GUI (e.g. "incorrect checksum", "unknown wordlist") should be treated as soft-errors, basically just warnings.

See e.g. #6860

The reasoning for making the errors ignorable is that there are many wordlists for bip39 (typically one per natural language) and we don't include those (or can reliably tell which language the presented seed is). The checksum is only checked against the English list.

The reasoning for making a distinction between the qt desktop gui and the qml android gui, is that on Android we force the user to use our custom keyboard anyway, while on desktop the input method is unrestricted. Using the custom keyboard pretty much would indirectly limit the user to English seeds in any case.