[release/7.0] [browser] make dynamic import cancelable

[pavelsavara]

Backport of #80257 to release/7.0

The underlying dynamic import() API of the browser is not cancelable.

During design of the C# API we added the cancelation token because we do that on all async methods.
We also added the C# code which would cancel/abandon the JS promise.
But we forgot to make the JS promise ready for that.
This PR fixes the omission.

It doesn't really cancel the JS download, nor execution of the module as that's not possible.
But it at least would stop blocking the caller.

Customer Impact

Fixes customer reported issue #80028

Testing

Unit test

Risk

Low, new API in Net7

[ghost]

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Backport of #80257 to release/7.0

Customer Impact

Fixes customer reported issue #80028

Testing

Unit test

Risk

Low, new API in Net7

Author:	pavelsavara
Assignees:	pavelsavara
Labels:	arch-wasm, area-System.Runtime.InteropServices.JavaScript
Milestone:	7.0.x

[carlossanlop]

Removing servicing-consider because the PR is still marked as draft. When ready, please re-add the label and send an email to Tactics requesting approval.

[pavelsavara]

The CI fail is unrelated here and re-run didn't help.
Is that OK @carlossanlop ?
If not, what's my next step ?

[carlossanlop]

@pavelsavara please make sure to fill out the template explaining how the issue affects customers and how the fix will address it. Once that's done, please send email to Tactics requesting merge approval,. and add the servicing-consider label. The Code Complete cut-off is on Friday 13th (less than 2 days from now), so we need to get this merged before EOD on Friday so that we have enough time to monitor the base branch in case anything breaks. Next weekend is a long weekend (Monday is a holiday in the US) so we are trying to avoid bottlenecks next week.

[carlossanlop]

The CI failure in dev-innerloop is known and unrelated: #80284

[pavelsavara]

Thanks, I updated the description.
It was already approved by email.

[carlossanlop]

Approved by Tactics via email (7.0.3).
Signed off by area owner.
CI failure unrelated.
No OOB changes needed (browser code).
Ready to merge.