Expose BaseUserTraits

[chenxzhang]

Per #1244, this PR exposes BaseUserTraits.

• I've included a changeset (psst. run yarn changeset. Read about changesets here).

[changeset-bot]

🦋 Changeset detected

Latest commit: a3c8b8f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@segment/analytics-core	Patch
@segment/analytics-next	Patch
@segment/analytics-node	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.87%. Comparing base (c0d58e3) to head (a3c8b8f).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1306   +/-   ##
=======================================
  Coverage   82.87%   82.87%           
=======================================
  Files         225      225           
  Lines        6019     6019           
  Branches     1365     1365           
=======================================
  Hits         4988     4988           
  Misses       1031     1031           

Flag	Coverage Δ
browser	92.21% <ø> (ø)
core	89.86% <ø> (ø)
node	87.93% <ø> (ø)

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[silesky]

Nit: The only package that you need to explicitly reference is core here, all dependent package will be bumped automatically by changesets. (cool, I know)