[FL-3847, FL-3513] Thread Signals (#3730)

* Add signal API
* Add signal support to loader
* Add signal support to ViewDispatcher
* Remove extra signal definitions
* Fix typos
  Co-authored-by: Silent <CookiePLMonster@users.noreply.github.com>
* scripts: runfap: close current app pre-launch
* loader: enable backlight when starting an app
* scripts: removed distfap.py
* Do not expose signal API via ViewDispatcher
* scripts: runfap: iterative retry to launch
* Add a loader signal subcommand
* Furi, Gui: move signal handling from View Dispatcher to Event Loop

Co-authored-by: Silent <CookiePLMonster@users.noreply.github.com>
Co-authored-by: hedger <hedger@nanode.su>
Co-authored-by: Aleksandr Kutuzov <alleteam@gmail.com>

scripts/runfap.py

@@ -2,6 +2,7 @@
 
 import operator
 from functools import reduce
+import time
 
 from flipper.app import App
 from flipper.storage import FlipperStorage, FlipperStorageOperations
@@ -9,6 +10,8 @@ from flipper.utils.cdc import resolve_port
 
 
 class Main(App):
+    APP_POST_CLOSE_DELAY_SEC = 0.2
+
     def init(self):
         self.parser.add_argument("-p", "--port", help="CDC Port", default="auto")
         self.parser.add_argument(
@@ -67,6 +70,23 @@ class Main(App):
                 if self.args.host_app:
                     startup_command = self.args.host_app
 
+                self.logger.info("Closing current app, if any")
+                for _ in range(10):
+                    storage.send_and_wait_eol("loader close\r")
+                    result = storage.read.until(storage.CLI_EOL)
+                    if b"was closed" in result:
+                        self.logger.info("App closed")
+                        storage.read.until(storage.CLI_EOL)
+                        time.sleep(self.APP_POST_CLOSE_DELAY_SEC)
+                    elif result.startswith(b"No application"):
+                        storage.read.until(storage.CLI_EOL)
+                        break
+                    else:
+                        self.logger.error(
+                            f"Unexpected response: {result.decode('ascii')}"
+                        )
+                        return 4
+
                 self.logger.info(f"Launching app: {startup_command}")
                 storage.send_and_wait_eol(f"loader open {startup_command}\r")