[FIX] mail: improve performance of JS write, especially for x2m

- store `x2many` values as `Set`. This is conceptually more correct because
  duplicates were already not allowed, and using a `Set` allows for much faster
  operations such as checking the presence of a record in the relation, which is
  done at every write, for every linked record.

- `stringify` in `write` was slow and unnecessary because we can always assume
  that new non-primitive should be provided to `write`

- remove field values from store, in favor of just storing a counter, which is
  enough to trigger renders. This allows to get rid of one Proxy level around
  data, which was slower, but which also prevented from using `Set`.

- write in store exactly once per update cycle, to trigger one `useStore` call
  on each component. Records keep `__state` but as a local counter, to let
  `useStore` know which records have been updated (easier to compare a counter
  than comparing each and every field value).

Results
=======

The worse case test (using a lot of x2m) that was used to benchmark this PR
`form_renderer_tests.js` of `mail_enterprise` went from taking around 4s before
this commit, to around 2.5s after this commit.
And the worse `_setRelationLinkMany2Many` previously took around 250ms, and it
now takes around 50ms.

The whole `mail` QUnit suite took around 55s before, now around 42s.

Part of task-2308312

closes odoo/odoo#55248

X-original-commit: 4db0a10d85534ef896f6bcbf13bca4983a6e2003
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/addons/mail/static/src/env/test_env.js b/addons/mail/static/src/env/test_env.js
index 75e921c27c7..b7bf22010cb 100644
--- a/addons/mail/static/src/env/test_env.js
+++ b/addons/mail/static/src/env/test_env.js
@@ -34,7 +34,9 @@ function addMessagingToEnv(providedEnv = {}) {
      */
     const store = new Store({
         env,
-        state: {},
+        state: {
+            messagingRevNumber: 0,
+        },
     });
 
     /**