Reduce use of DecodedInstruction in verifier.

This CL reduces the use of DecodedInstruction in verifier. It continues work
started in https://googleplex-android-review.googlesource.com/#/c/311171.

We cannot remove it completely from verifier because of method
MethodVerifier::VerifyInstruction. It is based on instruction flags rather than
instruction opcode. So we can't rely on instruction format. We may need to add
VRegA, VRegB and VRegC methods for this case. This should also be required for
the compiler itself. Let's delay this change to another CL.

Change-Id: I9d34df8b5bdb3db74e4959364c3cde90ef15585d
diff --git a/src/dex_instruction.h b/src/dex_instruction.h
index 218acb6..ae469d0 100644
--- a/src/dex_instruction.h
+++ b/src/dex_instruction.h
@@ -208,6 +208,7 @@
 
   // VRegA
   int8_t VRegA_10t() const;
+  uint8_t VRegA_10x() const;
   uint4_t VRegA_11n() const;
   uint8_t VRegA_11x() const;
   uint4_t VRegA_12x() const;