**Description:**
- `jsc.experimental.keepImportAssertions` is renamed to `jsc.experimental.keepImportAttributes`.
- `jsc.experimental.emitAssertForImportAttributes` is added.
**Related issue:**
- Closes#7908
- We don't need a list of bindings to check if an identifier is unresolved.
- Checking if an identifier is unresolved is now one CPU instruction.
- Previously it was one hashmap operation.
- This PR also improves performance, by removing the hashmaps mentioned above.