[FIX] mass_mailing: restore save on blur

Commit [1] defined a value for the `onWysiwygBlur` option of `Wysiwyg`
in the `mass_mailing` `html field`. This had the side effect of
overriding the value set by its parent `html field`, which was to call
`commitChanges`. As a result, the `mass_mailing` `html field` was not
saving its content on blur. This restores that behavior by explicitly
adding the call to `commitChanges` where it was missing.

[1]: https://github.com/odoo/odoo/commit/e212e873eb35eb9b9a931fb1521109475c008074

task-3288881

closes odoo/odoo#121231

X-original-commit: 817d494e4eaa29983f75d4f3d6754ef3c3cc6e51
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>
Signed-off-by: Antoine Guenet (age) <age@odoo.com>

addons/mass_mailing/static/src/js/mass_mailing_html_field.js

@@ -50,7 +50,10 @@ export class MassMailingHtmlField extends HtmlField {
             resizable: false,
             defaultDataForLinkTools: { isNewWindow: true },
             toolbarTemplate: 'mass_mailing.web_editor_toolbar',
-            onWysiwygBlur: () => this.wysiwyg.odooEditor.toolbarHide(),
+            onWysiwygBlur: () => {
+                this.commitChanges();
+                this.wysiwyg.odooEditor.toolbarHide();
+            },
             ...this.props.wysiwygOptions,
         };
     }