Upgrade minimal node support version to 14

[denysoblohin-okta]

• Set min supported Node version to 14
• Update broadcast-channel to ^4.14.0 (latest version depends on microtime 3.1.0 which requires Node 14)
• Don't use corejs: 3 in @babel/plugin-transform-runtime (was needed for Object.fromEntries which requires Node 12)
• microtime is a native module, needs to be built manually in Bacon setup script because of --ignore-scripts flag

Internal ref: OKTA-504784

Fixes https://github.com/okta/okta-auth-js/issues/1256

[codecov-commenter]

Codecov Report

Merging #1266 (5370362) into master (4cb6c6e) will decrease coverage by 1.49%. The diff coverage is 70.25%.

@@            Coverage Diff             @@
##           master    #1266      +/-   ##
==========================================
- Coverage   93.46%   91.96%   -1.50%     
==========================================
  Files         159      174      +15     
  Lines        4679     5055     +376     
  Branches     1081     1161      +80     
==========================================
+ Hits         4373     4649     +276     
- Misses        288      382      +94     
- Partials       18       24       +6     

Impacted Files	Coverage Δ
lib/idx/flow/AuthenticationFlow.ts	100.00% <ø> (ø)
lib/idx/types/api.ts	100.00% <ø> (ø)
lib/idx/types/idx-js.ts	100.00% <ø> (ø)
lib/options/index.ts	100.00% <ø> (ø)
lib/util/console.ts	54.16% <ø> (ø)
lib/myaccount/transactions/Base.ts	10.00% <10.00%> (ø)
lib/myaccount/transactions/EmailTransaction.ts	10.71% <10.71%> (ø)
lib/myaccount/transactions/PhoneTransaction.ts	13.04% <13.04%> (ø)
...yaccount/transactions/EmailChallengeTransaction.ts	17.64% <17.64%> (ø)
...b/myaccount/transactions/EmailStatusTransaction.ts	20.00% <20.00%> (ø)
... and 23 more

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