(new theory) Update TheoryFP to the new interface (#4953)

(new theory) Update TheoryFP to the new interface (#4953)

This updates the theory of floating points to the new interface (see #4929).

Notice that TheoryFP was not adding trigger terms to its equality engine (which should be done during notifySharedTerm), and thus was not propagating equalities between shared terms in combined theories. This PR updates its notifySharedTerm method to the default one.

FYI @martin-cs