[RISCV] Add more zext nneg tests. NFC

This adds additional tests for #82199.

These tests need us to propagate the nneg flag when we zero/sign
extend an existing zext nneg node. For these tests on RV64, call
lowering will need to sign extend or zero extend the existing zext
nneg to i64. getNode will fold this into a single zext. We should
propagate the nneg flag from the original zext nneg. This will allow
us to remove the zext nneg based on known sign bits during DAG combine.