[RISCV] Revise test coverage for shuffle/insert idiom which become v(f)slide1ups

This fixes a couple mistakes in 0f64d4f8.  In particular, I'd not included a negative test where the slideup didn't write the entire VL, and had gotten all of my 4 element vector shuffle masks incorrect so they didn't match.  Also, add a test with swapped operands for completeness.

The transform is in D151468.