Update Using Fonts page for 4.0

[Calinou]

Marked as draft as the section on emoji support needs to be completed. I'm waiting for godotengine/godot#64530 to be merged here, as it will ensure emoji support works better out of the box.

Edit: godotengine/godot#64530 is now merged, so this PR is ready for review. godotengine/godot#68995 will further improve usability, but I can open another PR to update the documentation as a follow-up.

[Calinou]

I've noticed that you need to double-click translations to add them, rather than single-clicking them. This doesn't seem logical to me, since there is no action that could otherwise be done by single-clicking. cc @bruvzg

[skyace65]

Two minor issues, but other than those this PR looks great!

[Calinou]

I improved the section on specifying character ranges using hexadecimal numbers or characters between single quotes:

godot-docs/tutorials/ui/gui_using_fonts.rst

Lines 95 to 103 in 592b777

	The **Character Ranges** option is an array that maps each position on the image
	(in tile coordinates, not pixels). The font atlas is traversed from left to
	right and top to bottom. Characters can be specified with decimal numbers
	(``127``), hexadecimal numbers (``0x007f``) or between *single* quotes
	(``'~'``). Ranges can be specified with a hyphen between characters.
	For instance, ``0-127`` (or ``0x0000-0x007f``) denotes the full ASCII range.
	As another example, ``' '-'~'`` is equivalent to ``32-127`` and denotes the range
	of *printable* (visible) ASCII characters.

Also, I've tested non-square bitmap fonts and can confirm they work, so I removed the line about the requirement for them to be square.