feat(widgets): add menu widget (#2603)

* add menu widget

* Update lv_example_widgets.h

* fix errors

* Update lv_menu.c

* try to fix errors

* micropython

* Fix colons

* Simplify and optimise

* Refactor

* Update lv_example_menu_3.c

* Update lv_example_menu_3.c

* Add simple micropython examples

* Improvements

* Automatically set clickable flags

* Custom header example

* Include example

* Refactor again

* Fix error

* Fix error

* Add back micropython example

* Hide back btn by default

* Add config

* Fix spacing

* Fix spacing

* Docs

* Update lv_theme_default.c

* Remove shaded text

* Improve clarity

* Create index.rst

* Update custom header example

* Change lv_menu_set_mode_sidebar to lv_menu_set_sidebar_page

* Fix unused variable

* Added ability to set title to page

* Flex

* Simplify sidebar check

* Rename mode and update header btn

* Run lv_conf_internal_gen.py

* Run code-format.sh

* Add contributors

* Micropython example 3

* Micropython example 4

* Improve docs

docs/widgets/extra/index.md

@@ -17,6 +17,7 @@
    keyboard
    led
    list
+   menu
    meter
    msgbox
    span

docs/widgets/extra/menu.md

@@ -0,0 +1,94 @@
+```eval_rst
+.. include:: /header.rst 
+:github_url: |github_link_base|/widgets/extra/menu.md
+```
+# Menu (lv_menu)
+
+## Overview
+The menu widget can be used to easily create multi-level menus. It handles the traversal between pages automatically.
+
+## Parts and Styles
+The menu widget is built from the following objects:
+- Main container: lv_menu_main_cont
+  - Main header: lv_menu_main_header_cont
+    - Back btn: [lv_btn](/widgets/core/btn)
+      - Back btn icon: [lv_img](/widgets/core/img)
+  - Main page: lv_menu_page
+- Sidebar container: lv_menu_sidebar_cont
+  - Sidebar header: lv_menu_sidebar_header_cont
+    - Back btn: [lv_btn](/widgets/core/btn)
+      - Back btn icon: [lv_img](/widgets/core/img)
+  - Sidebar page: lv_menu_page
+
+## Usage
+
+### Create a menu
+`lv_menu_create(parent)` creates a new empty menu.
+
+### Header mode
+The following header modes exist:
+- `LV_MENU_HEADER_TOP_FIXED` Header is positioned at the top.
+- `LV_MENU_HEADER_TOP_UNFIXED` Header is positioned at the top and can be scrolled out of view.
+- `LV_MENU_HEADER_BOTTOM_FIXED` Header is positioned at the bottom.
+
+You can set header modes with `lv_menu_set_mode_header(menu, LV_MENU_HEADER...)`. 
+
+### Root back button mode
+The following root back button modes exist:
+- `LV_MENU_ROOT_BACK_BTN_DISABLED`
+- `LV_MENU_ROOT_BACK_BTN_ENABLED`
+
+You can set root back button modes with `lv_menu_set_mode_root_back_btn(menu, LV_MENU_ROOT_BACK_BTN...)`.
+
+### Create a menu page
+`lv_menu_page_create(menu, title)` creates a new empty menu page.
+You can add any widgets to the page.
+
+### Set a menu page in the main area
+Once a menu page has been created, you can set it to the main area with `lv_menu_set_page(menu, page)`. NULL to clear main and clear menu history.
+
+### Set a menu page in the sidebar
+Once a menu page has been created, you can set it to the sidebar with `lv_menu_set_sidebar_page(menu, page)`. NULL to clear sidebar.
+
+### Linking between menu pages
+For instance, you have created a btn obj in the main page. When you click the btn obj, you want it to open up a new page, use `lv_menu_set_load_page_event(menu, obj, new page)`.
+
+### Create a menu container, section, separator
+The following objects can be created so that it is easier to style the menu:
+
+`lv_menu_cont_create(parent page)` creates a new empty container.
+
+`lv_menu_section_create(parent page)` creates a new empty section.
+
+`lv_menu_separator_create(parent page)` creates a separator.
+
+## Events
+- `LV_EVENT_VALUE_CHANGED` Sent when a page is shown.
+  - `lv_menu_get_cur_main_page(menu)` returns a pointer to menu page that is currently displayed in main.
+  - `lv_menu_get_cur_sidebar_page(menu)` returns a pointer to menu page that is currently displayed in sidebar.
+- `LV_EVENT_CLICKED` Sent when a back btn in a header from either main or sidebar is clicked. `LV_OBJ_FLAG_EVENT_BUBBLE` is enabled on the buttons so you can add events to the menu itself. 
+  - `lv_menu_back_btn_is_root(menu, btn)` to check if btn is root back btn
+
+See the events of the [Base object](/widgets/obj) too.
+
+Learn more about [Events](/overview/event).
+
+## Keys
+No keys are handled by the menu widget.
+
+Learn more about [Keys](/overview/indev).
+
+
+## Example
+
+```eval_rst
+.. include:: ../../../examples/widgets/menu/index.rst
+```
+
+## API 
+
+```eval_rst
+.. doxygenfile:: lv_menu.h
+  :project: lvgl
+        
+```