feat: detect one-theme as visual refresh via class and global flag

[mxschll]

*Issue #, if available: aQokArCTx9ab

Description of changes:

Recognize .awsui-one-theme as visual-refresh-compatible so vr components/layouts behave like vr when one-theme is active. Detection works via the .awsui-one-theme body class or global flag (window[Symbol.for("awsui-global-flags")].oneTheme).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.97%. Comparing base (eb4fa98) to head (b008169).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #221   +/-   ##
=======================================
  Coverage   98.97%   98.97%           
=======================================
  Files          44       44           
  Lines        1272     1273    +1     
  Branches      351      348    -3     
=======================================
+ Hits         1259     1260    +1     
  Misses         12       12           
  Partials        1        1           

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