Update libpng recipe and build SDL2_ttf vendored freetype with png support, so can render colored emoji

[misl6]

See: kivy/kivy#7565

Apple Color Emoji and other system fonts are not accessible on iOS, as are located outside of the app sandbox, so the user will need to use an alternative font ATM.

PS: Accessing the system fonts is feasible, via CGFont methods (by reconstructing a .ttf file), and we likely want to introduce this feature on kivy/kivy.

Demo:

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout


class UI(BoxLayout):
    pass


Builder.load_string(
    """
<UI>:
    Label:
        text: "😀 🎉 📷 👕 🐞"
        font_size: dp(80)
        font_name: "./NotoColorEmoji_WindowsCompatible.ttf"
"""
)


class Testapp(App):
    def build(self):
        return UI()


Testapp().run()

Output:

[AndreMiras]

Don't we want to make the {version} part of the url?

[misl6]

Moved to WIP, as I was supposed to change this URL to a non-mirror one, but I completely forgot. 🤦
Thank you for the heads up! (will handle it in a separate PR before this one gets merged)

(Our download process seems to not correctly handle a change that sourceforge recently performed)