Add section on "Oversampling" in fonts tutorial

**Your Godot version:**
4.3

**Issue description:**
Currently in the "Using Fonts" tutorial there are no information about "oversampling" at all. It is only present in the image description in the "MSDF font rendering"


I think this information would be quite useful especially that it allows to make text that uses small font size less blurry. (It was exactly my case with "Roboto" font. I couldn't use MSDF there because it caused "holes" in the font due to self-intersecting outlines in the font)

I would like to add that info myself but I'm not a pro at text rendering and I don't feel that I have enough knowledge to document how that setting works in Godot

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/tutorials/ui/gui_using_fonts.html#msdf-font-rendering