feat(label): added animation style property to apply it to circular scrolling animation of label widget (#3128)

* feat(label): added animation style property to apply it to circular scrolling animation of label widget

Added an animation style property to be used as animation template for different use cases in different widgets.
This commit implements using this property to set the start and repeat delay of the circular scrolling animation of the label widget.

Closes #3097

* fix(label): changed animation style property's var_type to `const lv_anim_t *`

* example(label): added example showing how to customize circular scrolling animation

* chore(label): ran code-format.py and added missing function prototype to lv_example_widgets.h

scripts/style_api_gen.py

@@ -344,6 +344,10 @@ props = [
  'style_type': 'num',   'var_type': 'lv_opa_t' ,  'default':'`LV_OPA_TRANSP`', 'inherited': 0, 'layout': 0, 'ext_draw': 0,
  'dsc': "The intensity of mixing of color filter."},
 
+ {'name': 'ANIM',
+ 'style_type': 'ptr',   'var_type': 'const lv_anim_t *',  'default':'`NULL`', 'inherited': 0, 'layout': 0, 'ext_draw': 0,
+ 'dsc': "The animation template for the object's animation. Should be a pointer to `lv_anim_t`. The animation parameters are widget specific, e.g. animation time could be the E.g. blink time of the cursor on the text area or scroll time of a roller. See the widgets' documentation to learn more."},
+
 {'name': 'ANIM_TIME',
  'style_type': 'num',   'var_type': 'uint32_t' ,  'default':0, 'inherited': 0, 'layout': 0, 'ext_draw': 0,
  'dsc': "The animation time in milliseconds. Its meaning is widget specific. E.g. blink time of the cursor on the text area or scroll time of a roller. See the widgets' documentation to learn more."},