Remove deprecated code 2021-04-21 (RobotLocomotion#15050)

Missed previously, perhaps owing to idiosyncratic date.

* drake::multibody::MultiBodyPlant::CalcCenterOfMassPosition
  * all overloads

pydrake: Replace "System YAML" with proper ".. pydrake_system::" dire…

…ctive (RobotLocomotion#14915)

* pydrake: Replace "System YAML" with proper ".. pydrake_system::" directive

Add script for building drake-visualizer on macOS (RobotLocomotion#14771

)

[FEM] Implement CorotatedModel and math helpers (RobotLocomotion#14599)

* Implement CorotatedModel and math helpers.

- Implement the fixed corotated model from Stomakhin, Alexey, et al.
 "Energetically consistent  invertible elasticity." Proceedings of the
 11th ACM SIGGRAPH/Eurographics conference on Computer Animation. 2012.

- Implement a few matrix calculation helpers to facilitate
 CorotatedModel.

- Refactor utility functions for St-Venant type constitutive models
 into free functions.

- Refactor LinearConstitutiveModelTest to test for both
 LinearConstitutiveModel and CorotatedModel.

Hotfix to repair asan failure in dynamic_elasticity_element_test (Rob…

…otLocomotion#14550)

Closes RobotLocomotion#14549. Relates RobotLocomotion#14533.

framework: Un-deprecate FixInputPort taking an const ref (RobotLocomo…

…tion#14454)

User-facing APIs should prefer const-ref (not unique_ptr) when the user
provides new values for the framework to use.  We will adjust the advice
in the class further in the future, but for now with a release in flight,
this is the minimal change to allow users to keep using the forward-
looking API.

Adds realsense-ros dependency for URDF and meshes (RobotLocomotion#14203

)

This commit provides Drake the ability to fetch the realsense-ros
upstream repository during build: IntelRealSense/realsense-ros:

- It gives Drake access to the realsense d415 xacro and mesh files

- After the download, xacro files are modified to cleanly stitch into
  a URDF in a Drake environment (rather than their native ROS
  environment)

- A test is provided that is closely based (copied + slightly modified)
  on the YCB meshes simple parsing tests

Add .png schematic and improved documentation to show Parent/Child bo…

…dies and joint M/F frames (aka Jp/Jc frames).

Name ports and add @System documentation for InverseDynamicsController (

RobotLocomotion#13879)

Performance tweak to MultibodyTree.CalcJacobianAngularAndOrTranslatio…

…nalVelocityInWorld (RobotLocomotion#13682)

- Change CalcJacobianAngularAndOrTranslationalVelocityInWorld to use auto for Eigen expressions and avoid common multiplication by the identity matrix.

- Add two more performance tweaks:
 -SpatialInertia.cast() no longer re-validates itself
 -Eliminate unnecessary matrix assignments in CalcJacobianTranslationalVelocityHelper