Umode assert
Created by: silabs-robin
Adding assertions for user mode, according to the reviewed and updated vplan (which will be pushed in separate PR).
Passes ci_check, except for "debug_test" which gets a miscompare (and I have not touched any relevant files).
Passes formal, except for 2 known RTL/RVFI problems, and 18 non-converging with a bound of >=35.