use libdl.so.2 instead of libdl.so for linux

This should fix builds on ubuntu-22.04.
- see https://stackoverflow.com/a/75855054
- see ied206/Joveler.DynLoader#1 for other dotnet library with the same issue

rcldotnet_common/DllLoadUtils.cs

@@ -54,10 +54,10 @@ public class DllLoadUtilsFactory {
       [DllImport ("kernel32.dll", EntryPoint = "FreeLibrary", SetLastError = true, ExactSpelling = true)]
       private static extern int FreeLibraryDesktop (IntPtr handle);
 
-      [DllImport ("libdl.so", EntryPoint = "dlopen")]
+      [DllImport ("libdl.so.2", EntryPoint = "dlopen")]
       private static extern IntPtr dlopen_unix (String fileName, int flags);
 
-      [DllImport ("libdl.so", EntryPoint = "dlclose")]
+      [DllImport ("libdl.so.2", EntryPoint = "dlclose")]
       private static extern int dlclose_unix (IntPtr handle);
 
       [DllImport ("libdl.dylib", EntryPoint = "dlopen")]
@@ -106,7 +106,7 @@ private static bool IsWindowsDesktop () {
 
       private static bool IsUnix () {
         try {
-          IntPtr ptr = dlopen_unix ("libdl.so", RTLD_NOW);
+          IntPtr ptr = dlopen_unix ("libdl.so.2", RTLD_NOW);
           dlclose_unix (ptr);
           return true;
         } catch (TypeLoadException) {
@@ -205,16 +205,16 @@ IntPtr DllLoadUtils.LoadLibrary (string fileName) {
 
     internal class DllLoadUtilsUnix : DllLoadUtils {
 
-      [DllImport ("libdl.so", ExactSpelling = true)]
+      [DllImport ("libdl.so.2", ExactSpelling = true)]
       private static extern IntPtr dlopen (String fileName, int flags);
 
-      [DllImport ("libdl.so", ExactSpelling = true)]
+      [DllImport ("libdl.so.2", ExactSpelling = true)]
       private static extern IntPtr dlsym (IntPtr handle, String symbol);
 
-      [DllImport ("libdl.so", ExactSpelling = true)]
+      [DllImport ("libdl.so.2", ExactSpelling = true)]
       private static extern int dlclose (IntPtr handle);
 
-      [DllImport ("libdl.so", ExactSpelling = true)]
+      [DllImport ("libdl.so.2", ExactSpelling = true)]
       private static extern IntPtr dlerror ();
 
       const int RTLD_NOW = 2;