Mono/C#: Several android fixes

- Added correct config file for android dllmaps.
- Fix __Internal DllImports with a dlopen fallback.
- Add missing P/Invoke functions and internal calls expected by the monodroid BCL and our custom version of the 'Android.Runtime.AndroidEnvironment' class (this last one can be found in the godot-mono-builds repo).
- Make sure to set 'btls' instead of 'legacy' as the default TLS provider on Android.

thirdparty/misc/ifaddrs-android.h

@@ -32,6 +32,11 @@
 // Fills out a list of ifaddr structs (see below) which contain information
 // about every network interface available on the host.
 // See 'man getifaddrs' on Linux or OS X (nb: it is not a POSIX function).
+// -- GODOT start --
+#ifdef __cplusplus
+extern "C" {
+#endif
+// -- GODOT end --
 struct ifaddrs {
   struct ifaddrs* ifa_next;
   char* ifa_name;
@@ -40,7 +45,21 @@ struct ifaddrs {
   struct sockaddr* ifa_netmask;
   // Real ifaddrs has broadcast, point to point and data members.
   // We don't need them (yet?).
+  // -- GODOT start --
+  // We never initialize the following members. We only define them to match the ifaddrs struct.
+  union
+  {
+    struct sockaddr *ifu_broadaddr;
+    struct sockaddr *ifu_dstaddr;
+  } ifa_ifu;
+  void *ifa_data;
+  // -- GODOT end --
 };
+// -- GODOT start --
+#ifdef __cplusplus
+}
+#endif
+// -- GODOT end --
 int getifaddrs(struct ifaddrs** result);
 void freeifaddrs(struct ifaddrs* addrs);
 #endif  // TALK_BASE_IFADDRS_ANDROID_H_