Add tests for text modules

[eemeli]

This is to support the spec changes in:

• tc39/proposal-import-text
• Add text imports whatwg/html#11933
• Add "text" destination type, for JavaScript text imports whatwg/fetch#1898
• Add "text" destination type, for JavaScript text imports w3c/webappsec-csp#794

I've effectively tried to duplicate and appropriately modify all the tests for JSON modules that I was able to find.

[bakkot]

Might consider adding a test that the request has a Sec-Fetch-Dest: text header. I think this is lacking for JSON as well, and have it on my backlog to write such a test, but as long as you're here...

Also, you could add a test that importing a module as JS, from a server which responds with valid JS file with a content type of text/javascript (and so loading succeeds), and then fetching it again with type: "text" causes two network requests (because the type is part of the module map). This is similar to repeated-imports.any.js but the other way around.

[eemeli]

Might consider adding a test that the request has a Sec-Fetch-Dest: text header. I think this is lacking for JSON as well, and have it on my backlog to write such a test, but as long as you're here...

Done. There are some test for the JSON module fetch headers already at fetch/metadata/tools/templates/script-json-module-import-static.sub.html; I added corresponding ones for text modules, as well as a non-generated test modeled after the audioworklet test.

Also, you could add a test that importing a module as JS, from a server which responds with valid JS file with a content type of text/javascript (and so loading succeeds), and then fetching it again with type: "text" causes two network requests (because the type is part of the module map). This is similar to repeated-imports.any.js but the other way around.

Done; added those to repeated-imports.any.js.

[bakkot]

New tests look great, thanks.

[annevk]

This feels needlessly inconsistent from the precedent that has been set for always decoding as UTF-8. Why account for the UTF-16 BOM when we don't account for many other things.

[eemeli]

You're right, this was a copy-paste error from the JSON module tests, which will consider these errors because they're not valid JSON. For text modules, we should get the file contents, parsed as UTF-8.

[annevk]

These look good to me. I didn't verify every line though.