super partition: mount super partitions using fs_mgr

We are now requiring fstab v2 for android-10+ trees. You can
specify twrp flags using /etc/twrp.flags to label and
annotate partitions.

This patchset uses fs_mgr to load the super partition and build
device mapper blocks off vendor and system depending on the slot
in use. These are mapped to partitions in TWRP and allowed to
be mounted read-only. The super partition is also mapped into a
TWRP partition in order to backup the entire partition. You cannot
backup individual device mapper blocks due to the device can only
be read-only. Therefore you cannot write back to the device mapper.

Change-Id: Icc1d895dcf96ad5ba03989c9bf759419d83673a3
diff --git a/twrp-functions.hpp b/twrp-functions.hpp
index 9d53ab6..412920a 100755
--- a/twrp-functions.hpp
+++ b/twrp-functions.hpp
@@ -67,7 +67,8 @@
 	static bool Path_Exists(string Path);                                       // Returns true if the path exists
 	static Archive_Type Get_File_Type(string fn);                               // Determines file type, 0 for unknown, 1 for gzip, 2 for OAES encrypted
 	static int Try_Decrypting_File(string fn, string password); // -1 for some error, 0 for failed to decrypt, 1 for decrypted, 3 for decrypted and found gzip format
-	static unsigned long Get_File_Size(const string& Path);                            // Returns the size of a file
+	static unsigned long Get_File_Size(const string& Path);                     // Returns the size of a file
+	static std::string Remove_Beginning_Slash(const std::string& path);        // Remove the beginning slash of a path
 	static std::string Remove_Trailing_Slashes(const std::string& path, bool leaveLast = false); // Normalizes the path, e.g /data//media/ -> /data/media
 	static void Strip_Quotes(char* &str);                                       // Remove leading & trailing double-quotes from a string
 	static vector<string> split_string(const string &in, char del, bool skip_empty);
@@ -113,6 +114,7 @@
 	static void check_selinux_support(); // print whether selinux support is enabled to console
 	static bool Is_TWRP_App_In_System(); // Check if the TWRP app is installed in the system partition
 	static int Property_Override(string Prop_Name, string Prop_Value); // Override properties (including ro. properties)
+	static void List_Mounts();
 	static void Copy_Log(string Source, string Destination);