Support passing arguments via serial CLI to external FAPs

[str4d]

All applications that aren't run on startup are required to have an entry point of the form int32_t entry_point(void* p):

flipperzero-firmware/scripts/fbt/appmanifest.py

Lines 354 to 357 in ccaa386

	def get_app_ep_forward(self, app: FlipperApplication):
	if app.apptype == FlipperAppType.STARTUP:
	return f"extern void {app.entry_point}();"
	return f"extern int32_t {app.entry_point}(void* p);"

This implies that some kind of context or arguments object is provided by the Flipper Zero to the app via the void* p. This appears to be the case for built-in apps; for example, the iButton app checks if p is a C string, and then parses it:

flipperzero-firmware/applications/main/ibutton/ibutton.c

Lines 313 to 336 in 224d0ae

	int32_t ibutton_app(void* p) {
	iButton* ibutton = ibutton_alloc();
	ibutton_make_app_folder(ibutton);
	bool key_loaded = false;
	bool rpc_mode = false;
	if(p && strlen(p)) {
	uint32_t rpc_ctx = 0;
	if(sscanf(p, "RPC %lX", &rpc_ctx) == 1) {
	FURI_LOG_D(TAG, "Running in RPC mode");
	ibutton->rpc_ctx = (void*)rpc_ctx;
	rpc_mode = true;
	rpc_system_app_set_callback(ibutton->rpc_ctx, ibutton_rpc_command_callback, ibutton);
	rpc_system_app_send_started(ibutton->rpc_ctx);
	} else {
	furi_string_set(ibutton->file_path, (const char*)p);
	if(ibutton_load_key_data(ibutton, ibutton->file_path, true)) {
	key_loaded = true;
	// TODO: Display an error if the key from p could not be loaded
	}
	}
	}

However, when running an external FAP from the serial CLI, providing arguments causes it to fail to start:

> loader open Applications /path/to/the.fap some args
// On screen
Error
Preload failed
Invalid file

Allowing arguments to be passed when starting via the serial CLI would enable external FAPs to act similarly to built-in CLI apps (albeit with the loader open Applications prefix).

Alternatively, if there were a way for an external FAP to register a CLI interface (like is often done in apps with type FlipperAppType.STARTUP), that would satisfy the use case. However, I suspect this would be trickier as it would require scanning the entire directory tree to find external FAPs to register in this way, so passing arguments directly to the external FAP is likely to be simpler.

[hedger]

Yep, we're also planning on implementing fixes to add RPC communication to .faps.

[str4d]

AFAICT this is supported after the FAP loader refactor in 0.86.1: because the loader is now doing the FAP loading, its argument handling Just Works. Thanks!