Test Mapping: Update test-mapping-group post platinum split

Platinum test-mapping suite is set to be expanded to other areas under Ironwood efforts. Since sysui covers the biggest fraction of total tests in platinum, splitting it as a separate suite will help me reduce load on total runtime of the suite while onboarding new tests and maintaining readability for non-experts.

Bug: 239384214
Bug: 239426163
Change-Id: I0f57deb2af3a943fda34d0ecaafb644afc67152c
Merged-IN: I0f57deb2af3a943fda34d0ecaafb644afc67152c
(cherry picked from commit 65f3aad581)

packages/SystemUI/TEST_MAPPING

@@ -91,7 +91,7 @@
   //
   // If you don't use @Staging or @Postsubmit, your new test will immediately
   // block presubmit, which is probably not what you want!
-  "platinum-postsubmit": [
+  "sysui-platinum-postsubmit": [
     {
       "name": "PlatformScenarioTests",
       "options": [
@@ -110,7 +110,7 @@
       ]
     }
   ],
-  "staged-platinum-postsubmit": [
+  "sysui-staged-platinum-postsubmit": [
     {
       "name": "PlatformScenarioTests",
       "options": [