Replace #apex with #systemapi

Currently, for an API symbol to be accessible to APEXes, it needs to be
marked as either # systemapi or # apex. It was originally just # apex,
but we added # systemapi to clearly identify the origin of the APIs.

The intended use is

* #apex is for APEX-visible symbols that are defined in an APEX
* #systemapi is for APEX-visible symbols that are defined in the
  platform (the non-updatable part)

This intention is documented build/soong/docs/map_files.md, but isn't
enforced at all.

With b/239274367, this is now enforced and therefore the #apex tags in
the platform library are replaced with `#systemapi`

This change does not alter any functionality.

Bug: 239274367
Test: m
Change-Id: I304e3982e6b70390d93bab63a1b9eb0c3571c596

libs/incident/libincident.map.txt

@@ -1,15 +1,15 @@
 LIBINCIDENT {
     global:
-        AIncidentReportArgs_init; # apex # introduced=30
-        AIncidentReportArgs_clone; # apex # introduced=30
-        AIncidentReportArgs_delete; # apex # introduced=30
-        AIncidentReportArgs_setAll; # apex # introduced=30
-        AIncidentReportArgs_setPrivacyPolicy; # apex # introduced=30
-        AIncidentReportArgs_addSection; # apex # introduced=30
-        AIncidentReportArgs_setReceiverPackage; # apex # introduced=30
-        AIncidentReportArgs_setReceiverClass; # apex # introduced=30
-        AIncidentReportArgs_addHeader; # apex # introduced=30
-        AIncidentReportArgs_takeReport; # apex # introduced=30
+        AIncidentReportArgs_init; # systemapi # introduced=30
+        AIncidentReportArgs_clone; # systemapi # introduced=30
+        AIncidentReportArgs_delete; # systemapi # introduced=30
+        AIncidentReportArgs_setAll; # systemapi # introduced=30
+        AIncidentReportArgs_setPrivacyPolicy; # systemapi # introduced=30
+        AIncidentReportArgs_addSection; # systemapi # introduced=30
+        AIncidentReportArgs_setReceiverPackage; # systemapi # introduced=30
+        AIncidentReportArgs_setReceiverClass; # systemapi # introduced=30
+        AIncidentReportArgs_addHeader; # systemapi # introduced=30
+        AIncidentReportArgs_takeReport; # systemapi # introduced=30
     local:
         *;
 };