[multibody] Add CurvilinearJoint (#22196)

[mshalm]

Adds a Joint and corresponding Mobilizer which model a single-DoF joint along a path composed of circular arcs and line segments within a plane, implementing part of #22196

Mobilizer is implemented as a thin wrapper around PiecewiseConstantCurvatureTrajectory. If the trajectory is a closed loop, the Joint can be flagged as periodic, in which case the mobilized frame can "wrap" around back to the beginning of the trajectory. In this case, the generalized coordinate q models the total distance traveled, with an intermediate function CurvilinearMobilizer::calc_s remapping to the trajectory's domain with drake::math::wrap_to.

The PR is longer than the recommended range of 500-1000 lines. We did not elect to split the PR into two due to the coupled nature of unit testing Joints and Mobilizers.

Some small touchups to PiecewiseConstantCurvatureTrajectory were included.

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This change is 

[jwnimmer-tri]

@drake-jenkins-bot ok to test

Thank you for this! I'll tag +@amcastro-tri to take a look and CC @sherm1 -- though I anticipate it'll probably be next week once people are back in-office before they dig in.

[amcastro-tri]

Thank you @mshalm! Today is my first day in the office after the holidays. I'll get back to you ASAP

Reviewable status: LGTM missing from assignee amcastro-tri, needs platform reviewer assigned, needs at least two assigned reviewers, missing label for release notes (waiting on @mshalm)