Update import defer tests for evaluation triggers

[nicolo-ribaudo]

Ref #4215.

This updates the tests that check what operations trigger evaluation of deferred modules, based on consensus in the last TC39 meeting. It's effectively what is included in tc39/proposal-defer-import-eval#53.

This PR doesn't include tests about what the results of those operations are (which will need to be tested for .then).

I suggest reviewing commit-by-commit:

• first the first one
• then the last one
• then the second one
• then the third one

All the tests are auto-generated from templates.

There is a bug with templates btw: their desc cannot start with [, because the generator will not escape/prefix it and so it becomes a Yaml array. I had to prefix all the descs with _ for this reason.

[takikawa]

I tried running this in my webkit prototype that's been updated to the new semantics, and as far as I can tell the test cases all run and agree with the implementation.