Rename "unsized" coercion as "unsizing"

[WaffleLapkin]

Built on top of #1731

[traviscross]

For whatever reason, "unsized coercion" feels more linguistically correct to me than "unsizing coercion". Here's one linguistic analog that perhaps underlies that feeling. We say "condo conversions" rather than "condoing conversions". The conversion makes the thing into a condo, so that's the kind of conversion that it is. Similarly, here, the coercion makes the thing unsized, so it's an unsized coercion.

[tshepang]

heh, "the coercion makes the thing unsized" explanation tells me unsizing coercion sound closer to what is meant

unsized coercion sounds like a coercion that happens to an unsized type (or to a type that may or may not be sized)

[traviscross]

Yes, I understand that as the motivation. I just can't find a lot of linguistic precedent for that reading in the context of converting things. E.g., "metric conversion" is to convert things to metric; it's a synonym for metrication. Similarly, if X is a religion, then an "X conversion" is a conversion to that religion. If I said we were doing an "octal conversion", I'd mean we were converting to octal; a "Markdown conversion" would be a conversion to Markdown. If we do a "prime factorization", it's the output rather than the input that is prime. The "red shift" (not "reddening shift") makes things appear more red. Etc.

[tshepang]

those other examples seems like they work due to convention, but they still feel not correct grammatically... they are ambiguous to those without context or experience