Allow overriding ro.debuggable to 1 on USER builds

When init found "/force_debuggable" in the first-stage ramdisk, it will
do the following if the device is unlocked:
  1. load /system/etc/adb_debug.prop (with ro.debuggable=1)
  2 .load userdebug_plat_sepolicy.cil instead of original plat_sepolicy.cil from
    /system/etc/selinux/.

This make it possible to run VTS on a USER build GSI, by using a special
ramdisk containing "/force_debuggable".

Bug: 126493225
Test: unlock a USER build device, check 'adb root' can work
Change-Id: I9b4317bac1ce92f2c0baa67c83d4b12deba62c92
diff --git a/init/property_service.cpp b/init/property_service.cpp
index 4bc857a..fc5538c 100644
--- a/init/property_service.cpp
+++ b/init/property_service.cpp
@@ -866,7 +866,7 @@
     }
 }
 
-void property_load_boot_defaults() {
+void property_load_boot_defaults(bool load_debug_prop) {
     // TODO(b/117892318): merge prop.default and build.prop files into one
     // We read the properties and their values into a map, in order to always allow properties
     // loaded in the later property files to override the properties in loaded in the earlier
@@ -888,6 +888,12 @@
     load_properties_from_file("/product_services/build.prop", nullptr, &properties);
     load_properties_from_file("/factory/factory.prop", "ro.*", &properties);
 
+    if (load_debug_prop) {
+        constexpr static const char kAdbDebugProp[] = "/system/etc/adb_debug.prop";
+        LOG(INFO) << "Loading " << kAdbDebugProp;
+        load_properties_from_file(kAdbDebugProp, nullptr, &properties);
+    }
+
     for (const auto& [name, value] : properties) {
         std::string error;
         if (PropertySet(name, value, &error) != PROP_SUCCESS) {