Split command into process and adb

The process API provides the system-specific implementation, the adb API
uses it to expose adb commands.

app/src/util/process.h

@@ -0,0 +1,73 @@
+#ifndef SC_PROCESS_H
+#define SC_PROCESS_H
+
+#include <stdbool.h>
+
+#include "config.h"
+
+#ifdef _WIN32
+
+ // not needed here, but winsock2.h must never be included AFTER windows.h
+# include <winsock2.h>
+# include <windows.h>
+# define PATH_SEPARATOR '\\'
+# define PRIexitcode "lu"
+// <https://stackoverflow.com/a/44383330/1987178>
+# define PRIsizet "Iu"
+# define PROCESS_NONE NULL
+# define NO_EXIT_CODE -1u // max value as unsigned
+  typedef HANDLE process_t;
+  typedef DWORD exit_code_t;
+
+#else
+
+# include <sys/types.h>
+# define PATH_SEPARATOR '/'
+# define PRIsizet "zu"
+# define PRIexitcode "d"
+# define PROCESS_NONE -1
+# define NO_EXIT_CODE -1
+  typedef pid_t process_t;
+  typedef int exit_code_t;
+
+#endif
+
+enum process_result {
+    PROCESS_SUCCESS,
+    PROCESS_ERROR_GENERIC,
+    PROCESS_ERROR_MISSING_BINARY,
+};
+
+// execute the command and write the result to the output parameter "process"
+enum process_result
+process_execute(const char *const argv[], process_t *process);
+
+// kill the process
+bool
+process_terminate(process_t pid);
+
+// wait and close the process
+bool
+process_simple_wait(process_t pid, exit_code_t *exit_code);
+
+// convenience function to wait for a successful process execution
+// automatically log process errors with the provided process name
+bool
+process_check_success(process_t proc, const char *name);
+
+#ifndef _WIN32
+// only used to find package manager, not implemented for Windows
+bool
+search_executable(const char *file);
+#endif
+
+// return the absolute path of the executable (the scrcpy binary)
+// may be NULL on error; to be freed by SDL_free
+char *
+get_executable_path(void);
+
+// returns true if the file exists and is not a directory
+bool
+is_regular_file(const char *path);
+
+#endif