Port generateSources to Scala 3 Library

[natsukagami]

The generators used in generateSources are copied over in the first commit, and changes to make them match the current source code is presented in the second commit.

This includes adding import scala.language.`2.13` into the generated sources.

It is added as a generateSources command inside scala-library-(non)boostrapped projects.

Note that the genprod file was renamed to GenerateLibraryNTemplates, but I still think the name is somewhat unclear. Suggestions welcomed.

[kyouko-taiga]

I left a few inline comments. Most of those relate to code style or comment consistency but I have some concerns about the logic of the function converters, which I found particularly difficult to follow.

[kyouko-taiga]

Suggested change

	def numeric = List(B, S, C, I, L, F, D)
	def values = List(U, Z) ++ numeric
	def numeric = List(B, S, C, I, L, F, D)
	def values = List(U, Z) ++ numeric

[kyouko-taiga]

Looks okay to me.

I think there is still a ton of inconsistent styling and dubious whitespaces but perhaps it is not worth dwelling on it. It would be nice if we could apply some automatic guidelines to address those 😔

[hamzaremmal]

I didn't want to port those generators as we don't change these files much and it will just make the build more complex. I'm against merging this for now as the added complexity in the build is not worth the benefits. Also, these files are fundamental to Scala 3 (and Scala 2) so if we were to modify them, it would be best to change them in Scala 2 and have them in Scala 3 when synchronising the files (unless the change is not compatible with Scala 2).

[hamzaremmal]

@natsukagami can we close this one too?