Support email verify callback

[aarongranick-okta]

• passes stateTokenExternalId to introspect
• allows shared storage without "oauth" flag (meant for legacy oauth cookies)
• clears shared storage if a matching state exists in sessionStorage
• do not bundle node-cache for browser version
• add _idxResponse to auth-js methods (to help widget conversion)
• separate shared storage for originalUri
• upgrades idx-js and fixes tests (no longer throws a "raw" idx response)
• shared storage is automatically enabled only in browser environment
• isInteractionRequired now supported on node platform
• updates express-embedded-auth-with-sdk sample:
  • handles email verify callback (on /login/callback)
  • displays more error types (instead of "Internal Error!")

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 92.45283% with 8 lines in your changes missing coverage. Please review.

Project coverage is 92.28%. Comparing base (2a753a0) to head (787f7af).
Report is 353 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/OktaAuth.ts	78.12%	7 Missing ⚠️
lib/idx/remediate.ts	90.00%	1 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #990   +/-   ##
=======================================
  Coverage   92.28%   92.28%           
=======================================
  Files         121      122    +1     
  Lines        3512     3566   +54     
  Branches      736      759   +23     
=======================================
+ Hits         3241     3291   +50     
- Misses        271      275    +4     

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