Enables view transition e2e tests with Firefox

[martrapp]

Changes

Adds e2e/view-transitions.test.js to playwright.firefox.config.js, see #11036.

=> e2e tests for view transitions will now not only run on Chrome, but also run on Firefox.

Our approach for counting full page loads during navigation was off by one as Firefox always generated an additional load for about:blank for each test case.

Few tests do not work the same or at all for simulated view transitions

• "No page rendering during swap()": Other than the native implementation, the simulation can not stop the renderer.
• "transition:name should be escaped correctly": setting view-transition-name w/o native support is a CSS error.
• "animation get canceled when view transition is interrupted": as entry animations run before exit animations in the simulation, only the entry animations get canceled.

Testing

e2e tests for view transitions now also run on Firefox.

Docs

/cc @withastro/maintainers-docs, I assume it is OK not to have changeset for this PR?

[changeset-bot]

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Latest commit: 8972fe4

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