Restore the .jar extension on the device side

Commit 3da95b52bd renamed
'scrcpy-server.jar' to 'scrcpy-server' to avoid issues on the client
side.

However, removing the extension may cause issues with app_process, so
restore the extension only on the device side.

Fixes <https://github.com/Genymobile/scrcpy/issues/944>

app/src/server.c

@@ -16,7 +16,7 @@
 #define SERVER_FILENAME "scrcpy-server"
 
 #define DEFAULT_SERVER_PATH PREFIX "/share/scrcpy/" SERVER_FILENAME
-#define DEVICE_SERVER_PATH "/data/local/tmp/" SERVER_FILENAME
+#define DEVICE_SERVER_PATH "/data/local/tmp/scrcpy-server.jar"
 
 static const char *
 get_server_path(void) {

server/src/main/java/com/genymobile/scrcpy/Server.java

@@ -7,7 +7,7 @@ import java.io.IOException;
 
 public final class Server {
 
-    private static final String SERVER_PATH = "/data/local/tmp/scrcpy-server";
+    private static final String SERVER_PATH = "/data/local/tmp/scrcpy-server.jar";
 
     private Server() {
         // not instantiable