CP-52880: Avoid O(N^2) behaviour in Xapi_vdi.update_allowed_operations

Activate old xapi_vdi.update_allowed_operations optimization: 
get_internal_records_where does a linear scan currently, so operating on N VDIs is O(N^2).

Look at the VBD records directly, like before this 2013 commit which regressed it:
5097475

(We are going to optimize get_record separately so it doesn't go through serialization)

For now only do this when run on the coordinator to avoid potentially large number of VBD
round-trip database fetches.
We'll need to optimize the 'get_internal_record_where' later to also speed up the pool case.

```
╭─────────────────────────────────┬───────────────────────────┬───────────────────────────┬───────────────────────────╮
│name                             │  major-allocated          │  minor-allocated          │  monotonic-clock          │
├─────────────────────────────────┼───────────────────────────┼───────────────────────────┼───────────────────────────┤
│  update_allowed_operations/VDI  │          9205.8042 mjw/run│        964577.0228 mnw/run│        2868770.0725 ns/run│
╰─────────────────────────────────┴───────────────────────────┴───────────────────────────┴───────────────────────────╯

update_allowed_operations/VDI (ns):
 { monotonic-clock per run = 2868770.072546 (confidence: 2947963.590731 to 2834338.835371);
   r² = Some 0.404284 }
```

Compared to the previous commit this is 18x faster.

Signed-off-by: Edwin Török <edwin.torok@cloud.com>

Author: edwintorok

ocaml/xapi/xapi_vdi.ml

@@ -476,6 +476,15 @@ let update_allowed_operations_internal ~__context ~self ~sr_records ~pbd_records
          )
   in
   let all = Db.VDI.get_record_internal ~__context ~self in
+  let vbd_records =
+    match vbd_records with
+    | None when Pool_role.is_master () ->
+        all.Db_actions.vDI_VBDs
+        |> List.rev_map (fun self -> Db.VBD.get_record_internal ~__context ~self)
+        |> Option.some
+    | v ->
+        v
+  in
   let allowed =
     let check x =
       match