Shenandoah is the only GC at this moment, that supports object pinning and string deduplication, we should add a test to ensure no regression of JDK-8269661.

JDK-8269661 did not show up in early tests are due to:
1) Majority strings are latin1
2) CompactString default to true

the combination results string values are never pinned, as GetStringCritical returns a inflated UTF16 copy instead of pinned string value.