Move functions from process to file

Move filesystem-related functions from process.[ch] to file.[ch].

app/src/util/file.h

@@ -0,0 +1,34 @@
+#ifndef SC_FILE_H
+#define SC_FILE_H
+
+#include "common.h"
+
+#include <stdbool.h>
+
+#ifdef _WIN32
+# define PATH_SEPARATOR '\\'
+#else
+# define PATH_SEPARATOR '/'
+#endif
+
+#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 free()
+char *
+get_executable_path(void);
+
+// Return the absolute path of a file in the same directory as he executable.
+// May be NULL on error. To be freed by free().
+char *
+get_local_file_path(const char *name);
+
+// returns true if the file exists and is not a directory
+bool
+is_regular_file(const char *path);
+
+#endif