Watchdog: break timeout loop via system fatal crash

Request system fatal crash via SysRq when a watchdog timeout loop is
detected. This escapes automatically the device hanging symptom and also
preserves context of system server in memory snapshot.

More details and background: go/break-sys-watchdog-loop

Bug: 141948707
Test: Insert 'sleep_forever()' to block BinderThreadMonitor to reproduce
      watchdog timeout.
Change-Id: I3ae4b33b0d7811764c61663ac3718311b55fd048

core/sysprop/Android.bp

@@ -19,3 +19,11 @@ sysprop_library {
     api_packages: ["android.sysprop"],
     vendor_available: false,
 }
+
+sysprop_library {
+    name: "com.android.sysprop.watchdog",
+    srcs: ["WatchdogProperties.sysprop"],
+    property_owner: "Platform",
+    api_packages: ["android.sysprop"],
+    vendor_available: false,
+}