Make the diagrams easier to edit

[MarkLodato]

As part of #360, clean up the Figma diagrams to make them easier to maintain and to use a consistent visual style.

Major changes:

• Re-implement the "supply chain model" diagram in the same visual style as the other diagrams. (Previously it was made in Google Drawings and looked very different.)
• Rename "bad dependency/package" to "risky dependency/package" as per Added revoked dependency threat #347. (@ThomasOwens FYI)

Minor visual changes:

• Switch font to Inter, which is a Google Web Font, from Prodigy Sans. This allows editing without installing the font locally, in particular enabling editing on Linux and Chromebook.
• Make the Package → Dependencies arrow dashed (liked the Dependencies box) to hint that a Dependency is itself a package.
• Use the hexagonal Build shape consistently. (In some versions it was an oval.)
• Adjust various alignments and spacings for consistency.
• Use white background color consistency. (In some versions it was transparent, which renders poorly on GitHub with dark mode.)

Invisible cleanups:

• Refactor the Figma file so that it's easier to maintain, and update the instructions to better explain how to use it.
• Remove the fonts from our repo, since they are no longer needed.
• Remove unused PNG file.

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[ThomasOwens]

I very much appreciate this. Anything to keep reducing the barrier of entry for people contributing is fantastic, and Figma was a big one for me (never having used it or done much with any kind of image editing at all before).

[joshuagl]

Looks like we completely lost the labels on docs/images/supply-chain-threats.svg, was that intentional?
There's a typo in docs/images/supply-chain-model.svg – depedencies --> dependencies

[MarkLodato]

Looks like we completely lost the labels on docs/images/supply-chain-threats.svg, was that intentional?

Reverted. It was intentional, but I shouldn't mix that into this refactoring PR. The diagrams are back to how they were before, and I'll send out a separate to consider removing them.

There's a typo in docs/images/supply-chain-model.svg – depedencies --> dependencies

Thanks, fixed.

[joshuagl]

LGTM, thanks for tackling this!

[MarkLodato]

Thanks for the review!