(coll) Inefficient calculation of power of two in HashMap

This is a SUNBUG for 100189: https://bugs.openjdk.java.net/show_bug.cgi?id=100189

Constructor does this:

public HashMap(int initialCapacity, float loadFactor) {
  ...
  int capacity = 1;
  while (capacity < initialCapacity)
      capacity <<= 1;
  ...
}

It is magnitude+ faster to do this:

static final double LOG2 = Math.log(2.0);
public HashMap(int initialCapacity, float loadFactor) {
  ...
  int capacity = 1 << ((int)Math.ceil(Math.log(initialCapacity)/LOG2 ));
  ...
}


Given the error checking in the head of the constructor, this code should just
plug-in.