Deno.exit permissions querying

### What problem are you trying to solve?

In Deno Deploy if I call `Deno.exit(1)` it throws a `PermissionDenied` error. This is fine and not unexpected but in other contexts I would like to be able to call `Deno.exit(1)` and so therefore I would like to do a runtime check to see if I have permission to call this function.

When I look at the [`PermissionsDescriptor`](https://deno.land/api@v1.36.0?s=Deno.PermissionDescriptor#typeAlias_PermissionDescriptor) type in the documentation there does not appear to be a descriptor available for the exit function but it seems like there should be.

Therefore this request is to add an `ExitPermissionDescriptor` which would have `name: "exit"` and can never be enabled via command line flags (aka --allow-exit is not a flag) and returns `"granted"` by default. But when queried in deno deploy would return `"denied"` for the permission state.

### Describe the solution you'd like

I would like a new permission to be added which deno deploy sets to denied so we can query for it.

### Describe alternatives you've considered

I can just try/catch the error as a workaround

I can also attempt to look in environment variables to detect that I'm running in Deno Deploy and then wrap the call to exit with logic which checks for those environment variables.

### Documentation, Adoption, Migration Strategy

```ts
const status = await Deno.permissions.query({ name: "exit" });
console.log(status.state); // denied when invoked in Deno Deploy
```

Begin with the Deno.permissions.query entry point and the linked PermissionsDescriptor documentation. Confirm the requested exit descriptor behavior across ordinary Deno and Deno Deploy contexts; done means the example query is supported and reports denied in Deno Deploy while remaining granted by default elsewhere.

Written by the indexing model from the issue text.