Skip unsupported texture formats

[andyleiserson]

Changes the readonly_and_readwrite_storage_textures test to check for feature support.

Issue: none

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Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located.
• Test descriptions are accurate and complete.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Tests avoid over-parameterization (see case count report).

When landing this PR, be sure to make any necessary issue status updates.

[github-actions]

Results for build job (at c318703):

 Test case/subcase counts did not change.

[kainino0x]

Hm........ in theory, the correct thing to do here would be to check wgslLanguageFeatures and not the device features. Because:

1. It's not just the new formats that should be skipped when the browser doesn't have support, it's also the existing formats that were newly-added to WGSL.
2. We should be running this test if the browser (compiler) supports the format, even if the device doesn't.

But we didn't add a wgsl language feature! Filed gpuweb/gpuweb#5524

[kainino0x]

Suggested change

	`Checks that the read and read_write access modes are only allowed with the language feature present
	TODO(https://github.com/gpuweb/gpuweb/issues/5524): Fix this to check wgslLanguageFeatures
	of the device features.
	`