Design tweaks of Fisher Factor classes. Now they don't declare ops in their construc...

Design tweaks of Fisher Factor classes.  Now they don't declare ops in their constructors, except possibly for making the cov variables (is this considered an op?).  This should allow for easier control over device placement of various ops in the future.

Fixed some problems with how colocations were done for ops computed in the base class and in the RNN class.

Colocations now controlled with global configuration variable (similar to the rest of the configuration of the FisherFactor classes).

PiperOrigin-RevId: 180441903