fix(auth): Preserve HostedUiException names under R8 in release builds

[VarshithaPamisetty]

Description:
On Android (release only), cancelling signInWithWebUI throws UrlLauncherException instead of UserCancelledException. R8 obfuscates HostedUiException$CANCELLED, so its simpleName no longer matches the "CANCELLED" code Dart checks. Fixed by shipping a consumer ProGuard rule (consumerProguardFiles) that keeps HostedUiException under R8.

Tests:
Verified e2e on a real Cognito Hosted UI (release): cancel → UrlLauncherException without the fix, UserCancelledException with it.

Before (no fix)	After (fix)

Fixes #6395

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.98%. Comparing base (473d812) to head (fc93d54).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7264   +/-   ##
=======================================
  Coverage   40.98%   40.98%           
=======================================
  Files         121      121           
  Lines        8273     8273           
  Branches     3598     3598           
=======================================
  Hits         3391     3391           
  Misses       4882     4882           

🚀 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.