Use libdl.dylib (not libdl.so) on Mac

[imnasnainaec]

No description provided.

[github-actions]

Test Results

       3 files  ±0     241 suites  ±0   5s ⏱️ -1s
   431 tests ±0     423 ✔️ ±0    8 💤 ±0  0 ❌ ±0 
1 309 runs  ±0  1 254 ✔️ ±0  55 💤 ±0  0 ❌ ±0 

Results for commit c283116. ± Comparison against base commit b990d03.

♻️ This comment has been updated with latest results.

[imnasnainaec]

Tested

		private const string DLFCN_NAME = "libdl.dylib";

		[DllImport(DLFCN_NAME, EntryPoint = "dlopen", SetLastError = true)]
		private static extern IntPtr dlopen_mac(string file, int mode);

in an isolated unit test on my Mac and it didn't error.

[ermshiperete]

On second thoughts: These changes shouldn't be necessary if the icu.net.dll.config file is in the same directory as icu.net.dll because it defines the mapping of libdl.so to libdl.dylib.