Rename XmlManifest.GetGroupsStr() to XmlManifest.GetManifestGroupsStr()

This makes it more clear what kind of groups it refers to.

Change-Id: I47369050d1436efcc77f3a69d5b7c99a536b23bc
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/528462
Tested-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

manifest_xml.py

@@ -1122,7 +1122,7 @@ https://gerrit.googlesource.com/git-repo/+/HEAD/docs/manifest-format.md
             groups += f",platform-{platform.system().lower()}"
         return groups
 
-    def GetGroupsStr(self):
+    def GetManifestGroupsStr(self):
         """Returns the manifest group string that should be synced."""
         return (
             self.manifestProject.manifest_groups or self.GetDefaultGroupsStr()