ART: Improve class initializer and constructor verification.

DEX file verifier checks additional properties of class initializers
and constructors:

(i) Names match expected <clinit> / <init>.
(ii) The method descriptor for <clinit> is ()V.
(iii) The return type of <init> is V.
(iV) No other names start with '<'.

Bug:  31313719
Change-Id: I60bffa6561e1bae353f97c42377ea556bfa790af
Test: m test-art-host-gtest-dex_file_verifier_test