src: allow embedders to disable esm loader

[codebytere]

This PR addresses a recent embedder-specific issue Electron is facing.

Blink has its own independent ESM loader, which is set up in the renderer process of Electron. When ESM was unilaterally unflagged, this meant that there would be two competing ESM loaders in the same process, both of which made assumptions about code being run.

For example, what can happen is that the devtools windows uses Node.js' implementation of the esmodule loader, which is at present incapable of loading modules from URLs (for good reason). This causes a bunch of devtools failures. There's no real way to specifically enable sandbox (and therefore force the Blink loader to take precedence) for devtools only, since at the time we're calling CreateContentRendererClient() we don't know what url we're loading (and therefore can't verify it's devtools or not). Thus, it makes more sense to allow embedders to specify that we don't want to register the ESM loader when creating an Environment via flag.

I also considered adding a new cli flag and just checking it via getOptionValue in pre_execution.js, but i think that (after chatting a bit with Anna) since this use case is quite specific to embedders that it makes more sense to make it an EnvironmentFlag. The only thing i wasn't sure of here was where specifically to expose it. I chose node_options but welcome any feedback or alternate preferences.

cc @addaleax

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

[devsnek]

Is it possible to add a test for this?

[codebytere]

@devsnek@addaleax i added two tests - i couldn't figure out how to do it any more simply so feel free to suggest alternatives or ways to simplify!

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/32116/ (:yellow_heart:)

[codebytere]

Landed in c23d2fd