[ADD] developer: scroller service added

This commit adds the documentation related to
the scroller service. This service is used for
the webclient to handle clicks on links and there
were no documentation related until now.

Author: Iucapad

content/developer/reference/frontend/services.rst

@@ -128,6 +128,8 @@ Reference List
      - manage the browser url
    * - :ref:`rpc <frontend/services/rpc>`
      - send requests to the server
+   * - :ref:`scroller <frontend/services/scroller>`
+     - handle clicks on anchors elements
    * - :ref:`title <frontend/services/title>`
      - read or modify the window title
    * - :ref:`user <frontend/services/user>`
@@ -692,6 +694,58 @@ When a rpc fails, then:
   displayed and the server is regularly contacted until it responds. The
   notification is closed as soon as the server responds.
 
+.. _frontend/services/scroller:
+
+Scroller service
+----------------
+
+Overview
+~~~~~~~~
+
+- Technical name: `scroller`
+- Dependencies: none
+
+Provides a way to handle scrolls to anchors in the webclient. 
+This service is used whenever a click occurs on the webclient.
+
+The service adds an event listener to get `click`'s on the document. The service is then
+checking if the selector contained in its href attribute is valid to distinguish anchors and Odoo 
+actions (e.g. ``<a href="#target_element"></a>``). It returns nothing if it is not the case.
+
+An event ``SCROLLER:ANCHOR_LINK_CLICKED`` is triggered on the main application bus. That event contains a
+custom event containing the `element` matching and its `id` to notify other parts that may need to handle 
+an anchor behavior themselves. The original event is also given as it might need to be prevented. Otherwise, 
+the ``scrollTo`` function is used to handle the scroll to the correct element directly in the service. 
+That function is imported from ``@web/core/utils/scrolling.js``.
+
+API
+~~~
+
+The following values are contained in the `anchor-link-clicked` custom event explained above.
+
+.. list-table::
+    :widths: 25 25 50
+    :header-rows: 1
+
+    * - Name 
+      - Type
+      - Description
+    * - ``element``
+      - ``HTMLElement | null``
+      - The anchor element targeted by the href
+    * - ``id``
+      - ``string``
+      - The id contained in the href
+    * - ``originalEv``
+      - ``Event``
+      - The original click event
+
+.. note::
+   The scroller service emits a `SCROLLER:ANCHOR_LINK_CLICKED` event on the :ref:`main bus <frontend/framework/bus>`
+   You should use `preventDefault()` on the event given to the listener element to avoid the service to handle the 
+   scrolling behavior and doing it correctly from the listener. It is used for example in the ``FormRenderer``
+   to set the notebook page visible before the scroll.
+
 .. _frontend/services/title:
 
 Title Service