Rename the server scrcpy-server.jar

The server is built as an APK to simplify the build, but in fact this is
a simple jar (it is not even signed).

In order to avoid confusion, rename it to .jar, so that users do not try
to "adb install" it.

Also rename it from "scrcpy" to "scrcpy-server" to distinguish from the
client-side.

Makefile

@@ -27,8 +27,8 @@ build-server:
 
 dist: build-server build-app
 	mkdir -p "$(DIST)/$(TARGET_DIR)"
-	# no need to sign the APK, we dont "install" it
-	cp server/build/outputs/apk/release/server-release-unsigned.apk "$(DIST)/$(TARGET_DIR)/scrcpy.apk"
+	# no need to sign the APK, we dont "install" it, this is in fact a simple jar
+	cp server/build/outputs/apk/release/server-release-unsigned.apk "$(DIST)/$(TARGET_DIR)/scrcpy-server.jar"
 	cp $(APP_BUILD_DIR)/scrcpy "$(DIST)/$(TARGET_DIR)/"
 
 dist-zip: dist

app/src/server.c

@@ -7,11 +7,11 @@
 #define SOCKET_NAME "scrcpy"
 
 process_t push_server(const char *serial) {
-    const char *apk_path = getenv("SCRCPY_APK");
-    if (!apk_path) {
-        apk_path = "scrcpy.apk";
+    const char *server_path = getenv("SCRCPY_SERVER_JAR");
+    if (!server_path) {
+        server_path = "scrcpy-server.jar";
     }
-    return adb_push(serial, apk_path, "/data/local/tmp/scrcpy.apk");
+    return adb_push(serial, server_path, "/data/local/tmp/scrcpy-server.jar");
 }
 
 process_t enable_tunnel(const char *serial, Uint16 local_port) {
@@ -29,7 +29,7 @@ process_t start_server(const char *serial, Uint16 max_size, Uint32 bit_rate) {
     sprintf(bit_rate_string, "%"PRIu32, bit_rate);
     const char *const cmd[] = {
         "shell",
-        "CLASSPATH=/data/local/tmp/scrcpy.apk",
+        "CLASSPATH=/data/local/tmp/scrcpy-server.jar",
         "app_process",
         "/", // unused
         "com.genymobile.scrcpy.ScrCpyServer",