Make layout use available image data before querying the image cache.
These changes make layout more efficient for any page which contains images that have already loaded, since it does not require synchronously querying the image cache thread for each image present. It also makes reloading a page actually display the images that are already in the image cache.
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#21919
- [x] There are tests for these changes
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Remove the HTMLTable{Header,Data}CellElement interfaces
Fixes#17222.
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This removes the `HTMLTableHeaderCellElement` and `HTMLTableDataCellElement` interfaces and uses the `HTMLTableCellElement` interface for both `th` and `td` elements, as per the spec.
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#17222.
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