Use libdl.so.2 when libdl.so is unavailable

[smoogipoo]

This is the bare minimum work required for this library to use libdl.so.2. The implementation is a copy of NativeLibraryLoader, an implementation that Veldrid uses. It does not use NativeLibrary because the project still targets netstandard1.4.

I originally intended to PR this upstream, but it looks like upstream is unmaintained because there was already another implementation aiming to fix the same thing that hasn't been merged in over a year. I didn't use that implementation because we don't target glibc v2.34.

So I've adjusted this to use the ppy prefix, and added tagged deploy, and intend to use it for our fork of Veldrid. It should be a once-off deploy and never touched again afterwards.

Sample deploy (failed due to no nuget perms): https://github.com/smoogipoo/vk/actions/runs/8713428105