Rename ApexName to ApexVariationName

In preparation for reusing the same variation for multiple apexes,
rename ApexName to ApexVariationName.

Bug: 164216768
Test: all soong tests
Change-Id: I88f2c5b192ffa27acd38e01952d0cefd413222a0
diff --git a/android/module.go b/android/module.go
index 6956167..04997c9 100644
--- a/android/module.go
+++ b/android/module.go
@@ -1331,7 +1331,7 @@
 		suffix = append(suffix, ctx.Arch().ArchType.String())
 	}
 	if apex, ok := m.module.(ApexModule); ok && !apex.IsForPlatform() {
-		suffix = append(suffix, apex.ApexName())
+		suffix = append(suffix, apex.ApexVariationName())
 	}
 
 	ctx.Variable(pctx, "moduleDesc", desc)