[FIX] web_editor: cache editor name_search/read across multiple m2o

The RPC that the m2o widgets used by snippet options make are cached at
the widget level. When two m2o widgets make the same RPC, they are
indeed made twice. This commit just move the cache outside of the
widget instance and thus makes it so the same RPC made across multiple
m2o are cached.

Note: this was particularly visible because all main snippets have the
"Conditional Visibility" option which uses 3 m2m widgets. At each drop
of such main snippet in the page, the option is created and the 3 m2m
widgets made their RPC. Then each further drop of snippet made the exact
same RPC for no good reason.
In the future, the system should be further improved to not require
those RPC on initial drop and clicks, especially as the "Conditional
Visibility" m2m widgets are hidden by default. This fix focuses on
fixing the generic m2m widgets.

closes odoo/odoo#102800

X-original-commit: 8e08c896df9ed5a7a0e559f1dbd8812f87908a39
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/web_editor/static/src/js/editor/snippets.options.js

@@ -2465,6 +2465,7 @@ const SelectPagerUserValueWidget = SelectUserValueWidget.extend({
     },
 });
 
+const m2oRpcCache = {};
 const Many2oneUserValueWidget = SelectUserValueWidget.extend({
     className: (SelectUserValueWidget.prototype.className || '') + ' o_we_many2one',
     events: Object.assign({}, SelectUserValueWidget.prototype.events, {
@@ -2482,7 +2483,7 @@ const Many2oneUserValueWidget = SelectUserValueWidget.extend({
     init(parent, title, options, $target) {
         this.afterSearch = [];
         this.displayNameCache = {};
-        this._rpcCache = {};
+        this._rpcCache = m2oRpcCache;
         const {dataAttributes} = options;
         Object.assign(options, {
             limit: '5',