Clean up dependencies, especially zlib-ng.

[kring]

This PR cleans up some weirdness I noticed while investigating the Android build failure in CesiumGS/cesium-unreal#1748.

We had our own custom find script for zlib-ng, even though it has its own. Perhaps we thought we needed it because we had the name of the import library wrong? Or perhaps the built-in one was added in a more recent vcpkg release? Either way, it's not needed anymore, so I removed it and fixed the library name (zlib-ng::zlib-ng -> zlib-ng::zlib).

Other changes:

• Removed a duplicate find_package for curl. Looks like a merge error.
• Fixed a typo.
• Sorted the find_package lines alphabetically.
• Updated Config.cmake.in with some recent third-party library changes. @timoore I'm not especially well equipped to test this one, so you should take a look and make sure I haven't broken something.

There's a cesium-unreal branch with the same name to demonstrate this still works ok in Unreal.

[j9liu]

Looks good @kring ! Though before I merge, I want to open a similar branch to check that Unity handles these changes well.

EDIT: branch here is passing 🙌

[j9liu]

Actually @timoore, per the PR description, you should take a look at this as well before merging.

[timoore]

@kring and @j9liu , this looks fine to me. It's too bad that library dependencies have to be tracked in both CMakeLists.txt and Config.cmake.in, but that's just the way it is... it's probably premature to have a common source for both.

[timoore]

Looks good, a positive change.

[j9liu]

Thanks @timoore !