toolbox: add setprop, start, and stop

Move these from toybox as they're Android specific and more easily
maintained here.

A few changes during the conversion:
* Report error in setprop if value is not a UTF8 string; this would
  previously fail only after attempting to set the property
* Inform users to check dmesg for further failure messages for all
  three programs
* Only start/stop zygote_secondary if the device is not single arch

Bug: 117321744
Bug: 133901248
Test: setprop works, start and stop work on single and multi-arch.

Change-Id: Id2194cf2b65221bde38aff91f0e86b33edb37f42
diff --git a/toolbox/Android.bp b/toolbox/Android.bp
index 5289976..9ca5607 100644
--- a/toolbox/Android.bp
+++ b/toolbox/Android.bp
@@ -28,6 +28,8 @@
         "toolbox.c",
         "getevent.c",
         "getprop.cpp",
+        "setprop.cpp",
+        "start.cpp",
     ],
     generated_headers: [
         "toolbox_input_labels",
@@ -40,6 +42,9 @@
     symlinks: [
         "getevent",
         "getprop",
+        "setprop",
+        "start",
+        "stop",
     ],
 }