Rename FIDL tables.c to old_tables.c (#795)

In fuchsia.git, we are moving FIDL coding table generation from fidlc to
fidlgen_hlcpp (https://fxbug.dev/39388). The first step of that is to
make fidlgen_hlcpp emit an empty tables.c: https://fxrev.dev/953989.
However, flutter is currently placing fidlc's table.c at the same path.
Renaming it to old_tables.c unblocks the soft transition.

build/fuchsia/sdk.gni

@@ -106,7 +106,9 @@ template("fuchsia_fidl_library") {
 
     inputs = [ invoker.meta ]
 
-    outputs = [ "$target_gen_dir/$library_name_slashes/cpp/tables.c" ]
+    # TODO(fxbug.dev/39388): These are the old coding tables generated by fidlc.
+    # Switch to the fidlgen_hlcpp coding tables.
+    outputs = [ "$target_gen_dir/$library_name_slashes/cpp/old_tables.c" ]
 
     args = [
       "--fidlc-bin",
@@ -118,7 +120,7 @@ template("fuchsia_fidl_library") {
       "--json",
       rebase_path("$target_gen_dir/$library_name_json"),
       "--output-c-tables",
-      rebase_path("$target_gen_dir/$library_name_slashes/cpp/tables.c"),
+      rebase_path("$target_gen_dir/$library_name_slashes/cpp/old_tables.c"),
     ]
 
     if (fuchsia_target_api_level != -1) {