Add a debug flag to convert all touch pointers to stylus

When the sysprop `persist.debug.input.simulate_stylus_with_touch`
is set, all pointers reported by TouchInputMapper will be converted
into stylus pointers.

Changes to the flag will require a reboot to take effect.

Bug: 217741685
Test: manual
Change-Id: I7723be718354872509a9e85beda10acdbe25dd48
diff --git a/services/inputflinger/reader/Android.bp b/services/inputflinger/reader/Android.bp
index 51546ce..3bd3275 100644
--- a/services/inputflinger/reader/Android.bp
+++ b/services/inputflinger/reader/Android.bp
@@ -71,6 +71,7 @@
         "libstatslog",
         "libui",
         "libutils",
+        "PlatformProperties",
     ],
     static_libs: [
         "libc++fs",