docs: fix links, add references, rename files (#5138)

docs/widgets/dropdown.rst

@@ -1,3 +1,6 @@
+.. _lv_dropdown:
+
+============================
 Drop-down list (lv_dropdown)
 ============================
 
@@ -15,6 +18,8 @@ The Drop-down list is added to the default group (if it is set). Besides
 the Drop-down list is an editable object to allow selecting an option
 with encoder navigation too.
 
+.. _lv_dropdown_parts_and_styles:
+
 Parts and Styles
 ****************
 
@@ -53,9 +58,13 @@ The list is hidden/shown on open/close. To add styles to it use
 
 Alternatively the theme can be extended with the new styles.
 
+.. _lv_dropdown_usage:
+
 Usage
 *****
 
+.. _lv_dropdown_options:
+
 Options
 *******
 
@@ -121,6 +130,8 @@ Manually open/close
 To manually open or close the drop-down list the
 ``lv_dropdown_open/close(dropdown)`` function can be used.
 
+.. _lv_dropdown_events:
+
 Events
 ******
 
@@ -136,6 +147,8 @@ See the events of the `Base object </widgets/obj>`__ too.
 
 Learn more about :ref:`events`.
 
+.. _lv_dropdown_keys:
+
 Keys
 ****
 
@@ -146,10 +159,14 @@ Keys
 
 Learn more about :ref:`indev_keys`.
 
+.. _lv_dropdown_example:
+
 Example
 *******
 
 .. include:: ../examples/widgets/dropdown/index.rst
 
+.. _lv_dropdown_api:
+
 API
 ***