feat(client): bring the error overlay to parity with webpack-dev-server

[bjohansebas]

• Render inside an about:blank iframe and style exclusively through the CSSOM so the overlay works under a strict style-src CSP; inline styles from ansi-html are re-applied via style.cssText.
• Support Trusted Types: innerHTML writes go through a policy (configurable via overlayTrustedTypesPolicyName).
• Capture uncaught runtime errors and unhandled rejections in the overlay (overlayRuntimeErrors, default true), with the same React error boundary heuristic as dev-server.
• Inline the HTML entity encoder and drop the html-entities dependency.
• Expose the overlay as a standalone subpath export (webpack-dev-middleware/client/overlay) so webpack-dev-server can reuse it.

Ref webpack/webpack-hot-middleware#457

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.23%. Comparing base (52f4d31) to head (9b8c387).

Additional details and impacted files

@@                Coverage Diff                 @@
##           hot-middleware    #2353      +/-   ##
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- Coverage           93.57%   93.23%   -0.34%     
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  Files                   4        4              
  Lines                1182     1182              
  Branches              354      354              
==================================================
- Hits                 1106     1102       -4     
- Misses                 68       72       +4     
  Partials                8        8              

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