[refactor] Split watchdog in a standalone library for reuse

This simplifies the task of creating an independent library of
rkpd_client later.

Test: atest keystore2_test
Bug: 241428146
Change-Id: I2834c9be9f5100d52829e6392f0dd48e7c76beb1
diff --git a/keystore2/Android.bp b/keystore2/Android.bp
index 271f94d..dd036c2 100644
--- a/keystore2/Android.bp
+++ b/keystore2/Android.bp
@@ -61,6 +61,7 @@
         "libserde_cbor",
         "libthiserror",
         "libtokio",
+        "libwatchdog_rs",
     ],
     shared_libs: [
         "libcutils",