[X86][SSE] Added truncated vector arithmetic tests.

For cases where we are truncating an integer vector arithmetic result, it may be better to pre-truncate the input operands - no code to support this yet (scalar is done with SimplifyDemandedBits but adding vector support could be a lot of work) but these tests represent the current codegen status.

Example bugs: PR14666, PR22703

llvm-svn: 263384