Add Generic Binding<Cost> and Binding<Constraint> to vertices and edges within a GcsTrajectoryOptimization::EdgesBetweenSubgraphs

[cohnt]

Closes #21981.

This PR builds off of #22179, so let's hold off on feature review until that lands. (I'll update this branch based on any changes made to that PR before it merges.)

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This change is 

[cohnt]

Now that #22179 has gone to platform review, let's go ahead and start feature review here.

+@RussTedrake, let's finish this chain of PRs off?

[RussTedrake]

One minor request, otherwise
+@sammy-tri for platform review, please.

Reviewed 3 of 5 files at r1, 2 of 2 files at r2, all commit messages.
Reviewable status: 1 unresolved discussion, LGTM missing from assignee sammy-tri(platform), commits need curation (https://drake.mit.edu/reviewable.html#curated-commits) (waiting on @cohnt)

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planning/trajectory_optimization/gcs_trajectory_optimization.h line 759 at r2 (raw file):

                    kRestriction});

    /** Convenience overload of AddEdgeCost to take in a Binding<Cost>. */

i think it's worth still mentioning here that the binding can only use the placeholder variables (since they enter slightly differently)

[cohnt]

Reviewable status: 1 unresolved discussion, LGTM missing from assignee sammy-tri(platform), commits need curation (https://drake.mit.edu/reviewable.html#curated-commits) (waiting on @cohnt)

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planning/trajectory_optimization/gcs_trajectory_optimization.h line 759 at r2 (raw file):

Previously, RussTedrake (Russ Tedrake) wrote…

i think it's worth still mentioning here that the binding can only use the placeholder variables (since they enter slightly differently)

Done.

I also made the change to the analogous methods for Subgraph.

[RussTedrake]

Reviewed 1 of 1 files at r3, all commit messages.
Reviewable status: LGTM missing from assignee sammy-tri(platform), commits need curation (https://drake.mit.edu/reviewable.html#curated-commits) (waiting on @cohnt)

[sammy-tri]

I ran out of time to get to this today, but I'll keep it assigned to me for platform review since I'm familiar (a bit) with the area from previous PRs. Sorry for the delay!

Reviewable status: LGTM missing from assignee sammy-tri(platform), commits need curation (https://drake.mit.edu/reviewable.html#curated-commits) (waiting on @cohnt)

[sammy-tri]

+(status: squashing now)

Reviewed 3 of 5 files at r1, 1 of 2 files at r2, 1 of 1 files at r3, all commit messages.
Reviewable status: complete! all discussions resolved, LGTM from assignees sammy-tri(platform),RussTedrake(platform)