kcmdlinectrl: define system property for kcmdlinectrl

This defines the kcmdline_prop context for properties controlled by
kcmdlinectrl, and defines a property called kcmdline.binder for
switching between the Rust and C implementations of the Binder driver.

It is intended that additional kcmdline properties introduced in the
future would share the same kcmdline_prop context.

Test: Verified that setprop/getprop work and that the value is loaded properly at boot
Bug: 326222756
Change-Id: Iea362df98d729ee110b6058c6e5fa6b6ace03d8e
diff --git a/private/property_contexts b/private/property_contexts
index 7e31dd7..cb22d64 100644
--- a/private/property_contexts
+++ b/private/property_contexts
@@ -893,6 +893,11 @@
 arm64.memtag.         u:object_r:arm64_memtag_prop:s0 prefix string
 persist.arm64.memtag. u:object_r:arm64_memtag_prop:s0 prefix string
 
+# kcmdline props for dogfood experiments
+# All kcmdline properties share the kcmdline_prop context
+kcmdline.loaded     u:object_r:kcmdline_prop:s0 exact bool
+kcmdline.binder     u:object_r:kcmdline_prop:s0 exact enum c rust
+
 net.redirect_socket_calls.hooked u:object_r:socket_hook_prop:s0 exact bool
 
 # Settings system properties containing mutable "global" device settings.