Allow checking for existence without showing Biometry UI

[Marcocanc]

We can check if biometry protected items exist without prompting for authentication by disabling Authentication UI and checking for errSecInteractionNotAllowed

[Marcocanc]

Any chance to get this merged, @kishikawakatsumi?

[james-rant]

This looks like a good addition to me. Would be good to see it merged.

[codecov]

Codecov Report

Merging #384 into master will decrease coverage by 44.21%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master     #384       +/-   ##
===========================================
- Coverage   90.83%   46.61%   -44.22%     
===========================================
  Files           1        1               
  Lines        1767     1757       -10     
===========================================
- Hits         1605      819      -786     
- Misses        162      938      +776

Impacted Files	Coverage Δ
Lib/KeychainAccess/Keychain.swift	46.61% <100%> (-44.22%)	⬇️

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[kishikawakatsumi]

Thanks for the PR! This PR is superseded #451