MethodHandles: Unhide java.lang.invoke.*

A handful of methods are not implemented yet, and remain hidden.
Javadoc @links that reference these hidden methods have temporarily
been converted to @code.

The only notable Android specific change is the changing of link
targets from a method in the MethodHandles class to another method in
the same class to remove the explicit class reference (e.g.
{@link MethodHandles#lookup} -> {@link #lookup}). This is to work around
javadoc errors caused by these links

Test: make docs
Change-Id: Ie7a49b76de59ea957e117cb695a28cb1137dae4e