Cleanup make MacroElements from Elements

This change involves several classes that require being added to a
Figure. Since these classes follow the `render` semantics of a
MacroElement it makes more sense to make them also inherit from
MacroElement.

Excluded from this change is actually making use of
the template mechanics of the MacroElement.

folium/elements.py

@@ -1,12 +1,12 @@
 from typing import List, Tuple
 
-from branca.element import CssLink, Element, Figure, JavascriptLink, MacroElement
+from branca.element import CssLink, Figure, JavascriptLink, MacroElement
 
 from folium.template import Template
 from folium.utilities import JsCode
 
 
-class JSCSSMixin(Element):
+class JSCSSMixin(MacroElement):
     """Render links to external Javascript and CSS resources."""
 
     default_js: List[Tuple[str, str]] = []

folium/features.py

@@ -101,7 +101,7 @@ def __init__(
         )
 
 
-class Vega(JSCSSMixin, Element):
+class Vega(JSCSSMixin):
     """
     Creates a Vega chart element.
 
@@ -193,6 +193,8 @@ def render(self, **kwargs) -> None:
             name=self.get_name(),
         )
 
+        # TODO: this could be rewritten to use the facilities of MacroElement
+        # and the facilities of JSCSSMixin
         figure = self.get_root()
         assert isinstance(
             figure, Figure
@@ -224,7 +226,7 @@ def render(self, **kwargs) -> None:
         )
 
 
-class VegaLite(Element):
+class VegaLite(MacroElement):
     """
     Creates a Vega-Lite chart element.
 
@@ -297,6 +299,9 @@ def render(self, **kwargs) -> None:
             name=self.get_name(),
         )
 
+        # TODO: this could be rewritten to use the facilities of MacroElement
+        # and the facilities of JSCSSMixin
+
         figure = self.get_root()
         assert isinstance(
             figure, Figure

folium/map.py

@@ -409,7 +409,7 @@ def render(self) -> None:
         super().render()
 
 
-class Popup(Element):
+class Popup(MacroElement):
     """Create a Popup instance that can be linked to a Layer.
 
     Parameters