Move inputflinger_tests to platinum-postsubmit

And also, move libinput_tests to platinum staging, since they are also fundamental to how input operates.

Bug: 274115727
Change-Id: I115e945cd08ddbbef0083dca84860eaf140949a9
Test: presubmit
diff --git a/services/inputflinger/TEST_MAPPING b/services/inputflinger/TEST_MAPPING
index af9d2eb..10fec74 100644
--- a/services/inputflinger/TEST_MAPPING
+++ b/services/inputflinger/TEST_MAPPING
@@ -298,9 +298,14 @@
       "name": "CtsInputRootTestCases"
     }
   ],
-  "staged-platinum-postsubmit": [
+  "platinum-postsubmit": [
     {
       "name": "inputflinger_tests"
     }
+  ],
+  "staged-platinum-postsubmit": [
+    {
+      "name": "libinput_tests"
+    }
   ]
 }