fix(auth): Remove online check from getCurrentUser

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available: #3118

Description of changes:
Removes the check for expired refresh tokens from the getCurrentUser call. None of the other Amplify platforms had this check, so this better aligns with their implementations.

Now getCurrentUser will be a simple offline-only check to see if there are cached credentials on the device. If there are, we return the user data.

This does mean that in cases where you were signed in but your refresh tokens have expired (or were revoked) getCurrentUser will now succeed, where previously it would have failed.

How did you test these changes?

• Revoked users tokens, ensured that getCurrentUser still succeeds.

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Ensure commit message has the appropriate scope (e.g fix(storage): message, feat(auth): message, chore(all): message)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 54.25%. Comparing base (3f72bcb) to head (2d2a977).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3122      +/-   ##
==========================================
- Coverage   54.27%   54.25%   -0.02%     
==========================================
  Files        1038     1038              
  Lines       31991    32006      +15     
  Branches     4700     4703       +3     
==========================================
+ Hits        17363    17365       +2     
- Misses      12788    12802      +14     
+ Partials     1840     1839       -1     

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