Adopt Rapid's sidewalk and curb mapping improvements to iD

[tordans]

Context

Rapid recently added a few improvements to make it easier to map sidewalks, crossings and curbs.

Here is a first list take from the changelog:

• Add curbs feature spits out error facebook/Rapid#1654, Add default "sidewalk" tags when connectedWayTags is null facebook/Rapid#1671 Fix: Crash when adding curbs if there is no connected sidewalk - "this.tags is null"
• "Missing curb nodes" when kerbs are tagged with kerb=no facebook/Rapid#1657 Fix: Don't suggest curb nodes when they are already mapped with kerb=no
• Do not use "unspecified" for kerb, use kerb=yes facebook/Rapid#1672 Fix: Unspecified curb should be kerb=yes, not kerb=unspecified
• Add validation to create kerb nodes for pedestrian crossings.  facebook/Rapid#1460, Kerb Validator  facebook/Rapid#1583, Kerb Validator Findings and Suggestions facebook/Rapid#1619, Curb validator fixes facebook/Rapid#1622 Add a new 'Curb Nodes' suggestion to suggest and add curb nodes
• Suggested crossing node at endpoint of crossing line facebook/Rapid#1597, Fix Crossing Tag Suggestions for Road-Connected Nodes facebook/Rapid#1599 Fix: Don't suggest converting a crossing endpoint into a crossing node

Goal

I wonder which of those improvements would be a good addition to iD. We should test them, collect feedback and specify which we would like to backport to iD.

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There are other, related PRs in iD that we should keep in mind as well, especially #10524 and maybe #10256

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FYI I added this as a suggestion for a GSoC Project (as a packages with #10743): https://wiki.openstreetmap.org/wiki/Google_Summer_of_Code/2025/Project_ideas#iD_editor