fix(ngOptions): use reference check only when not using trackBy

Change the check on changed value for ngOptions to ensure that a reference check is only done
when trackBy is not used.  Previously, if trackBy was being used but the values of the objects were
equal a reference check was then used which would cause the check to be true if the objects had
different memory references but the values were equal.  This can cause issues with forms being
marked dirty when the value of the model as not actually changed.

Closes #11936
Closes #11996