apex: mount up apex files into /sbin for library access

This patch uses the loop device to mount files under
/sbin/ from /system/apex in order for the device to
use libraries or other files store inside these files.

Each apex file is mounted over a loop device into a
directory correpsonding to the apex filename under
/sbin/.

Once apex mounting is completed, TWRP will set a
property twrp.apex.loaded to true so that init
can use them as a LD_LIBARY_PATH source.
Change-Id: I69f14a969123ac9cf1afc85b6cf76836cb092fb2

Change-Id: Ica6a7d8e479bcaec8bec4483b5e8d2b45ee105fb

twrp.cpp

@@ -51,6 +51,7 @@ extern "C" {
 #include "openrecoveryscript.hpp"
 #include "variables.h"
 #include "twrpAdbBuFifo.hpp"
+#include "twrpApex.hpp"
 #ifdef TW_USE_NEW_MINADBD
 // #include "minadbd/minadbd.h"
 #else
@@ -376,12 +377,17 @@ int main(int argc, char **argv) {
 	// Check if system has never been changed
 	TWPartition* sys = PartitionManager.Find_Partition_By_Path(PartitionManager.Get_Android_Root_Path());
 	TWPartition* ven = PartitionManager.Find_Partition_By_Path("/vendor");
-
 	if (sys) {
 		if (sys->Get_Super_Status()) {
 			if (!PartitionManager.Prepare_All_Super_Volumes()) {
 				LOGERR("Unable to prepare super volumes.\n");
 			}
+			sys->Mount(true);
+			twrpApex apex;
+			if (!apex.loadApexImages()) {
+				LOGERR("Unable to load apex images from %s\n", APEX_DIR);
+			}
+			property_set("twrp.apex.loaded", "true");
 		} else {
 			if ((DataManager::GetIntValue("tw_mount_system_ro") == 0 && sys->Check_Lifetime_Writes() == 0) || DataManager::GetIntValue("tw_mount_system_ro") == 2) {
 				if (DataManager::GetIntValue("tw_never_show_system_ro_page") == 0) {