[Web] Ensure editor crossorigin isolation headers

[adamscott]

Follow-up to #86089.

An error prevents the registration of the service worker for the editor Web build.

This PR ensures that ___GODOT_ENSURE_CROSSORIGIN_ISOLATION_HEADERS___ is being replaced in the service worker for the editor build.

[akien-mga]

Code seems ok to me, but adding this kind of build option seems really niche. I don't fully understand who would use this option and when?

[adamscott]

Code seems ok to me, but adding this kind of build option seems really niche. I don't fully understand who would use this option and when?

The issue right now is that the editor build is somewhat broken. And I don't like the idea of enforcing COI headers for editor builds.

[akien-mga]

Code seems ok to me, but adding this kind of build option seems really niche. I don't fully understand who would use this option and when?

The issue right now is that the editor build is somewhat broken. And I don't like the idea of enforcing COI headers for editor builds.

Why do we need a compile time option for this instead of just performing this change if env.editor_build is True?

[adamscott]

You're right. The SW even checks for the headers before applying them, so if the server is already setup, no cry no foul.

[adamscott]

@akien-mga I simplified the PR, I enforce the placeholder to be true, without any build variable.

[Calinou]

Looks good to me. The rationale makes sense to me as threads are a hard requirement for the web editor.

[Faless]

LGTM

[Repiteo]

Thanks!