sysprop_library: Rename system scope to public

In the first design, public sysprops have been accessible from Java
modules linking against SDK. But SDK modules shouldn't do, because
sysprop_library isn't for the apps. This renames system to public, so
that only public(System till now) and internal scopes remain from now.

Bug: 131637873
Test: m && sysprop_test
Change-Id: I548007d4a6018922f98d3d13915cee1d66070086

cc/library.go

@@ -882,10 +882,10 @@ func (library *libraryDecorator) link(ctx ModuleContext,
 			isVendor := ctx.useVndk()
 			isOwnerPlatform := Bool(library.Properties.Sysprop.Platform)
 
-			useSystem := isProduct || (isOwnerPlatform == isVendor)
+			usePublic := isProduct || (isOwnerPlatform == isVendor)
 
-			if useSystem {
-				dir = android.PathForModuleGen(ctx, "sysprop/system", "include").String()
+			if usePublic {
+				dir = android.PathForModuleGen(ctx, "sysprop/public", "include").String()
 			}
 		}