Create new top-level dir, OWNERS for CSS Layout API (#9183)

This is for being able to write web-platform-tests for the CSS Layout API[1]

[1] https://drafts.css-houdini.org/css-layout-api/
diff --git a/css/css-layout-api/OWNERS b/css/css-layout-api/OWNERS
new file mode 100644
index 0000000..ade6708
--- /dev/null
+++ b/css/css-layout-api/OWNERS
@@ -0,0 +1,2 @@
+@bfgeek
+@tabatkins