dillon1000/react

Replace NodePath with SourceLocation

Removes all the `path: NodePath` values from various IR node types, replacing 
them with `loc: SourceLocation`. This type is an alias for babel's source 
location type plus a "generated" variant. The "OtherStatement" kind also used 
the `path` to print back the original AST (since we don't look into these); 
instead, we now capture the underlying `node` and emit that as-is during 
codegen. 

While I was doing this, i also fixed up the places where we had passed a null 
path; the vast majority have a clear place we can pull a location from. For 
example, `a ?? b` syntax creates some places/instructions for the `a != null`, 
but those can all point back to the `a` location.