ENH: linspace behavior for timedelta_range and interval_range
 Behavior similar to `np.linspace` has been implemented for the regular `date_range` function in #20846, e.g. `pd.date_range(start='2018-01-01', end='2018-01-10', periods=50)`. 

This behavior is not supported by `timedelta_range` or `interval_range`, so it seems like it should be added for consistency with `date_range`.

Note that this behavior doesn't really make sense for `period_range` since a frequency is always required.   Likewise it doesn't really make sense for `bdate_range`, as the only distinguishing feature from `date_range` is the support for custom business day logic, and the default freq being `'B'`, both of which imply a frequency.  Doubly so for `cdate_range`, as it's been deprecated in favor of `bdate_range`.
