[Kernel] Adds test skeleton of module Linear_filter.

tests/float/linear_filter_test.i

+/* run.config
+   MODULE: @PTEST_NAME@
+   OPT:
+*/
+/* run.config*
+   DONTRUN:
+*/

tests/float/linear_filter_test.ml

+(* Programmatic tests of the invariant computation of linear filters by the
+   module Linear_filter. Run by linear_filter_test.i. *)
+
+let main _ =
+  ()
+
+let () = Db.Main.extend main

tests/float/oracle/linear_filter_test.res.oracle

+[kernel] Parsing linear_filter_test.i (no preprocessing)