Add template for GetScopedFrameByName

[marip8]

Is your feature request related to a problem? Please describe.

I have written a few custom constraint evaluators that need to extract a Frame from a MultibodyPlant of type AutoDiffXd. When using these constraint evaluators with more complex plants with nested models, I hoped to use the GetScopedFrameByName utility but found that (as of v1.36.0) it only works with plants of type double.

Describe the solution you'd like
It would be helpful for the GetScopedFrameByName utilities to be template functions that work with all plant types.

- const drake::multibody::Frame<double>* GetScopedFrameByNameMaybe(
+ template<typename T>
+ const drake::multibody::Frame<T>* GetScopedFrameByNameMaybe(
-    const drake::multibody::MultibodyPlant<double>& plant,
+    const drake::multibody::MultibodyPlant<T>& plant,
    const std::string& full_name);

- const drake::multibody::Frame<double>& GetScopedFrameByName(
+ template<typename T>
+ const drake::multibody::Frame<T>& GetScopedFrameByName(
-    const drake::multibody::MultibodyPlant<double>& plant,
+    const drake::multibody::MultibodyPlant<T>& plant,
    const std::string& full_name);

I personally am also using the Python interface, so it would also be helpful for this change to propagate there too.

Describe alternatives you've considered
I'm currently writing my own helper function to do this, but it would be cleaner for this functionality to exist out of the box with Drake

Additional context

Related to #15660