[IMP] web: use showSearchInput in model field selector

The option `showSearchInput`, which is used on the model field selector to display a search
input that filters the displayed fields, is not set by default.

This includes the model field selector instantiated in the `domain` field widget.

closes odoo/odoo#29986

addons/web/static/tests/fields/basic_fields_tests.js

@@ -5164,7 +5164,7 @@ QUnit.module('basic_fields', {
     });
 
     QUnit.test('basic domain field usage is ok', function (assert) {
-        assert.expect(6);
+        assert.expect(7);
 
         this.data.partner.records[0].foo = "[]";
 
@@ -5205,6 +5205,9 @@ QUnit.module('basic_fields', {
         assert.ok($fieldSelectorPopover.is(":visible"),
             "field selector popover should be visible");
 
+        assert.containsOnce($fieldSelectorPopover, '.o_field_selector_search input',
+            "field selector popover should contain a search input");
+
         // The popover should contain the list of partner_type fields and so
         // there should be the "Color index" field
         var $lis = $fieldSelectorPopover.find("li");