ART: String intrinsics for Mterp interpreter

Adds the most common java.lang.string intrinsics.  Includes change
to jvalue handling to zero-exend setting of chars and booleans to
64 bits (aligns with current sign-extension of shorts and ints).

Bug: 30933338

Benchmarks:
  2x boost for Caffeinemark String
  11% improvement for Dhrystone

Test: ART_TEST_INTERPRETER=true m test-art-host
Test: ART_TEST_INTERPRETER=true m test-art-target (Bullhead)

Note: Added intrinsics have existing test coverage via
082-inline-execute and 123-inline-execute2.

Change-Id: I64b35b1d7bdfe14da0c662594c0edf5cde667277