Build shared library for Apple Silicon

[rob-odwyer]

This adds support for an aarch64 build of the shared library, and updates the NativeLibraryLoader to load it on macOS when the os.arch system property is aarch64.

Although it's pretty straightforward to build for this architecture, running the tests is a lot more complex so I've disabled them when cross-compiling for now. It looks like bytecodealliance/wasmtime uses qemu to solve this problem for some architectures, but it's not as simple as just setting a target.

[kawamuray]

Thanks for the PR! Left some comments.

Apple sillicon support has been strongly demanded so this would be appreciated by many :) #36

Btw I'm wondering if this issue has been fixed: #36 (comment)
Apparently it did? as in this PR already passing CI.

[rob-odwyer]

Updated the build.gradle and the loading logic to use the following paths (grabbed these from a tagged build on the fork to confirm):

$ file jni-libs/*
jni-libs/libwasmtime_jni_0.17.0_linux_x86_64.so:     ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=fe48cb0c3ace952c7619e0e498399475cf0ddd98, with debug_info, not stripped
jni-libs/libwasmtime_jni_0.17.0_macos_aarch64.dylib: Mach-O 64-bit dynamically linked shared library arm64
jni-libs/libwasmtime_jni_0.17.0_macos_x86_64.dylib:  Mach-O 64-bit dynamically linked shared library x86_64
jni-libs/wasmtime_jni_0.17.0_windows_x86_64.dll:     PE32+ executable (DLL) (GUI) x86-64, for MS Windows

On #36 - I think my timing was just lucky! I didn't run into any cross-compilation issues, so it must have been fixed upstream.

[kawamuray]

LGTM, thanks!