Implementation of CredentialManagement wrapping feature

[TMSCH]

List of changes:

• Cleaned up exposed OpenYolo API so that return value of Promise resolution are non null. Errors should be used instead.
• Updated logic to respect the cleaned up API.
• Removed the wrapBrowserRequest logic from the initialization. Instead using a per request logic that can be triggered with a browserWrappingRequired error.
• Refactored errors to not subclass the JS Error class as the prototype is not extendable and it can lead to unexpected behavior in compiled code.
• Creation of a no-op navigator.credentials wrapper for browser without it.
• Added better tests coverage for api.ts file.
• Some syntax cleanup, made navigator_credentials.ts file to use await construct instead of Promise syntax.
• Expose a subset of OpenYoloInternalError on openyolo_spi namespace so that providers' implementations' can return specific errors (noCredentialsAvailable, userCanceled, browserWrappingRequired)
• I had to manually write a subset of the CredentialManagement API externs as I couldn't find any in our own codebase or externally...

Please review very carefully. I tested the code with Smart Lock implementation with success.

[codecov-io]

Codecov Report

Merging #43 into master will increase coverage by 4.24%. The diff coverage is 94.4%.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
+ Coverage   87.26%   91.51%   +4.24%     
==========================================
  Files          34       34              
  Lines        1429     1449      +20     
  Branches      168      176       +8     
==========================================
+ Hits         1247     1326      +79     
+ Misses        182      123      -59

Impacted Files	Coverage Δ
ts/protocol/rpc_messages.ts	100% <ø> (+4.61%)	:arrow_up:
ts/api/provider_frame_elem.ts	61.9% <ø> (ø)	:arrow_up:
ts/protocol/errors.ts	93.02% <100%> (+3.99%)	:arrow_up:
ts/api/hint_request.ts	100% <100%> (ø)	:arrow_up:
ts/api/api.ts	92.65% <100%> (+22.97%)	:arrow_up:
ts/api/credential_request.ts	100% <100%> (ø)	:arrow_up:
ts/spi/spi.ts	100% <100%> (ø)	:arrow_up:
ts/api/exports.ts	100% <100%> (ø)
ts/spi/provider_frame.ts	87.4% <87.5%> (+1.47%)	:arrow_up:
ts/api/navigator_credentials.ts	92.63% <88.46%> (+2.49%)	:arrow_up:
... and 5 more

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[TMSCH]

Tests coverage is >90%! :D

[TMSCH]

Thanks Rahul!

[TMSCH]

Thanks Iain!