Move all tests using import assertions to files named as such

[nicolo-ribaudo]

Extracted from #3843. I need this commit as a common base for two PR:

• add import attributes tests
• update import assertions tests after the recent normative changes (in the past 6 months)

[nicolo-ribaudo]

CI is failing because gralljs 23 changed the name of their release artifacts (now the folder is prefixed as graal-23.0.0 and not vm-23.0.0), and esvu does not support it yet.

https://github.com/oracle/graaljs/releases/tag/graal-23.0.0

[linusg]

GraalJS should not even run as part of CI anymore (a858077), you might need to rebase the PR

[ptomato]

I had a question about some of the tests that look like they would be common to both import assertions and import attributes, such as the trailing comma in import('foo',). @nicolo-ribaudo explained to me that we'll get duplicate tests for these (1) because they are generated anyway and (2) because there is no way to express "import-assertions OR import-attributes" in the feature flags.

Since this is blocking other PRs, I'll go ahead and merge it.