RFR: Cherry-pick: 8213473: Replace testB_mem_imm matcher with testUB_mem_imm plus Shenandoah parts

[Roman Kennke]

This seems an obvious fix in hindsight, but somehow we did not
originally make it ;-)

In order to reduce mess when merging from upstream, I'd like to
cherry-pick "8213473: Replace testB_mem_imm matcher with testUB_mem_imm"
and remove the Shenandoah parts from mulnode.cpp

Testing: tier3_gc_shenandoah

Ok?