Problem/Motivation
From #3202016-30: Let GDToolkit support AVIF image format:
ToolkitGdTest::testManipulations()is a monster that dates back to simpletest when multiple tests were performed in a single method to avoid multiple installations. In the era of Kernel tests, it's better split it in more understandable bits.
This entire class dates back to Simpletest times, today we can use data providers and have more atomic tests.
Steps to reproduce
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Proposed resolution
Modernize the test.
Remaining tasks
User interface changes
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API changes
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Data model changes
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Release notes snippet
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