Merge changes from topic "openjdk11-java.lang.String-strip"

* changes:
  OpenJDK 11: Merging in java.lang.String (strip*() methods)
  OpenJDK 11: Merging in java.lang.String (concat() tests)
  OpenJDK 11: Merging in java.lang.String (import string compaction tests)
  OpenJDK 11: Merging in java.lang.String (fix split() fast path)