FloatBuffer, DoubleBuffer are missing hashCode() methods

[niloc132]

Additionally equals and hashcode where they are present have incorrect Javadoc - they suggest that position and limit are not considered when comparing values, contrary to the implementation and specification. Note that this will not be reflected in generated docs (as these are emulated GWT/j2cl classes), but should be updated.

These types correctly have equals() implemented, but are missing their hashCode(), potentially leading to situations where two instances might be considered "equal" to each other, yet not have their hashcode match.

At a glance, behavior of hashcode seems unspecified, I'd be inclined to lean on the java.util.Arrays.hashCode() methods a sub-view, and some casting trickery to implement these.