Only show the reauth modal if a primary 2FA provider is enabled

[adamwoodnz]

Fixes #160

This checks whether the Two_Factor_Totp is available before showing the reauth modal.

In the current state the backup codes are still accessible, but I believe the intention with #47 is to disable access to that screen as well if the Two_Factor_Totp provider is unavailable, see #157

[pkevan]

While this would solve the current setup, I don't think we necessarily want to limit this to just TOTP since we are introducing webauthn too and that would require another fix here - is there any alternative method?

[iandunn]

I don't think we necessarily want to limit this to just TOTP since we are introducing webauthn too and that would require another fix here - is there any alternative method?

#157 introduces a primaryProviderEnabled bool in AccountStatus. If that'd be useful here too, we could maybe move it into script.js, and then add it to GlobalContext so AccountStatus can reuse it.

[iandunn]

I think the root cause for this is actually an upstream bug. I've opened WordPress/two-factor#565 and WordPress/two-factor#566 for that.

I think that will fix this, but haven't tested yet since it's still a WIP.

[dd32]

This works for me, although I've added a few comments on the method of checking, since I think it'd be better to intersect arrays rather than checking for specific keys

[iandunn]

LGTM 👍🏻