Migrations:
- Error registration no longer required for Interrupted or BadResource
(these are core exception)
- `include_js_files!`/`ExtensionFileSource` changes
Adds `runtime/shared.rs` which is imported by both `build.rs` and the
rest of the crate, containing utilities used by both.
Renames the `snapshot_from_snapshot` feature to
`exclude_runtime_main_js` since that's what it does and it's relevant
outside of snapshotting when `__runtime_js_sources` is specified.
