method handles should have a collectArguments transform, generalizing asCollector

Currently, a method handle can be transformed so that multiple arguments are collected and passed to the original method handle. However, the two routes to doing this are both limited to special purposes.

(They are asCollector, which collects only trailing arguments, and only into an array; and foldArguments, which collects only leading arguments into filter function, and passes both the filtered result *and* the original arguments to the original.)

MethodHandles.collectArguments(mh, pos, collector) should produce a method handle which acts like lambda(a*, b*, c*) { x = collector(b*); return mh(a*, x, c*) }, where the span of arguments b* is located by pos and the arity of the collector.

There is internal machinery in any JSR 292 implementation to do this. It should be made available to users.

This is a missing part of the JSR 292 spec.