Replace String CharArray with internal uint16_t array.

Summary of high level changes:
  - Adds compiler inliner support to identify string init methods
  - Adds compiler support (quick & optimizing) with new invoke code path
    that calls method off the thread pointer
  - Adds thread entrypoints for all string init methods
  - Adds map to verifier to log when receiver of string init has been
    copied to other registers. used by compiler and interpreter

Change-Id: I797b992a8feb566f9ad73060011ab6f51eb7ce01
diff --git a/test/021-string2/expected.txt b/test/021-string2/expected.txt
index bd7f049..a9c6eb8 100644
--- a/test/021-string2/expected.txt
+++ b/test/021-string2/expected.txt
@@ -1 +1,2 @@
 Got expected npe
+OK