Add libpalmrejection_test to inputflinger presubmit

The libpalmrejection library is going to be used in the input code, so
let's run the libpalmrejection_test unit test whenever we change input
code to prevent regressions.

Bug: 198472780
Test: cd services/inputflinger && atest
Change-Id: I4fabb51395b758c578bdef967899c76d17959c18
diff --git a/services/inputflinger/TEST_MAPPING b/services/inputflinger/TEST_MAPPING
index 3d85bef..9b72ff4 100644
--- a/services/inputflinger/TEST_MAPPING
+++ b/services/inputflinger/TEST_MAPPING
@@ -15,6 +15,9 @@
       "name": "inputflinger_tests"
     },
     {
+      "name": "libpalmrejection_test"
+    },
+    {
       "name": "InputTests"
     },
     {