dillon1000/react

[be] Fix missing break and update no-fallthrough eslint rule

- Fixes a missing break in InferTypes - I disabled no-fallthrough previously 
because it would erroneously report that certain cases with non-builtin throws 
(eg `invariant`) would fall through. This brings the rule back but allows 
disabling it with a `// break omitted` comment, since it's still helpful in 
catching some actual missing breaks.