🐛 Support stylesheet serialization in Safari iOS 16.x

[bcaudan]

Motivation

Since the bump of safari iOS version, one test is failing inconsistently:

 serializeDocumentNode handles
    with dynamic stylesheet
      ✗ serializes a document with adoptedStyleSheets [Mobile Safari 16.4 (iOS 16.4.1)]
	Expected $.adoptedStyleSheets.length = 0 to equal 1.

It seems that Safari started the adoptedStyleSheets implementation with FrozenArray around 16.x version.

• ObservableArray, and its use by adoptedStyleSheets · Issue #693 · w3ctag/design-reviews
• Instead of assignable FrozenArray, use add / remove · Issue #45 · WICG/construct-stylesheets
• adoptedStyleSheets (ObservableArray) has non-writable length

In this case, the use of map simply returns an empty array without any error.

Changes

Use a regular for loop to iterate over CSSStyleSheet array.

Test instructions

I've managed to see the fix working where the issue should have happened.
We should not see this test fail anymore.

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[sethfowler-datadog]

LGTM!