creating workflow for mirror::String compression

All-ASCII String characters are stored in 8-bit blocks
instead of 16-bit. The compression has not taken place, but all
workflow are in the code already (changing kUseStringCompression in
string.h file to TRUE will enable the feature)

Notes: Feature works on interpreter only without optimizing

Test art: m ART_TEST_INTERPRETER=true ART_TEST_OPTIMIZING=false
          test-art-host

Also tested with String tests from libcore/:
1. libcore.java.lang.StringTest
2. libcore.java.lang.StringBufferTest
3. libcore.java.lang.StringBuilderTest
4. libcore.java.lang.OldStringTest
5. libcore.java.lang.OldStringBufferTest

Memory improvement is 33% (from 6.03% to 4.03%, total String memory
from all apps per total memory of all apps) measured on Angler
with Hprof tools

Bug: 31040547
Change-Id: I9cc92c265ebf1305fc06b5fc33efd83797660cce
diff --git a/runtime/arch/stub_test.cc b/runtime/arch/stub_test.cc
index 80bb51d..10adb3a 100644
--- a/runtime/arch/stub_test.cc
+++ b/runtime/arch/stub_test.cc
@@ -1203,6 +1203,7 @@
 
 
 TEST_F(StubTest, StringCompareTo) {
+  TEST_DISABLED_FOR_STRING_COMPRESSION();
   // There is no StringCompareTo runtime entrypoint for __arm__ or __aarch64__.
 #if defined(__i386__) || defined(__mips__) || \
     (defined(__x86_64__) && !defined(__APPLE__))