[sgen] Fix bridge interop missing some xrefs due to improve registration.
* sgen-bridge.c: Split the registration and dfs1 steps so we avoid issues
where an earlier entry that points to a later one would not have a xref
created between them.
First we insert all bridges into the hash table and then we do dfs1.
It must be done in 2 steps since the bridge arrays doesn't come in reverse topological order,
which means that we can have entry N pointing to entry N + 1.
If we dfs1 entry N before N + 1 is registered we'll not consider N + 1 for this bridge
pass and not create the required xref between the two.