Mark ctx.expand_locations parameter short_paths as undocumented

Usage of the parameter is private to builtins and a few other packages as part of Starlarkification and not intended for public use.

PiperOrigin-RevId: 509816292
Change-Id: I43f4656ca0101b067f94c3888625861d73bf9ea5

src/main/java/com/google/devtools/build/lib/starlarkbuildapi/StarlarkRuleContextApi.java

@@ -500,8 +500,9 @@ String expandMakeVariables(
         @Param(
             name = "short_paths",
             named = true,
+            positional = false,
             defaultValue = "False",
-            doc = "Use root relative paths instead of full exec paths"),
+            documented = false),
       },
       allowReturnNones = true,
       useStarlarkThread = true)