ART: Add getDeclaredConstructor cutout for unstarted runtime

In the vein of getDeclaredMethod and getDeclaredField. Refactor
code from java_lang_Class to share code.

Allows to compile-time initialize:
* sun.security.x509.AVAKeyword
* sun.security.x509.X500Name

Bug: 27265238
Change-Id: I075c1b11f3408f5b31e4f84140a24fd8d3eaa17e