Use metadata directory instead of re-extracting every launch

[PaintNinja]

This addresses the todo comment inside SlimeLauncher's main class. Needs the complimenting FG7 PR to work: MinecraftForge/ForgeGradle#1084

[LexManos]

I think because both FG and FDP use this, and having to update both is a pain.
The better option would be to continue to support the input as a zip, but supporting a directory.
I am also not a fan of Gradle's zipTree as it extract EVERYTHING in the zip to disc twice while doing the extract for the specific files you want. So its rather slow.

But, I think the better way to address the TODO would just to skip extracting entirely. Instead just reading the file from the zip to memory using JsonData.minecraftVersion(InputStream)

I think the TODO itself, is just old, as the FG side doesn't extract the archive anymore.
I'm wrong on that

[PaintNinja]

Answered in the FG PR, reiterating here for clarity if someone refers back to this: worst case it extracts twice on Gradle side on setup but then no longer has to re-extract on SlimeLauncher side every run after that, best case it doesn't have to extract at all because it's cached on Gradle side and SlimeLauncher's directly fed the extracted directory.

I've restored support for the metadata.zip path now