R1:f6621a5fdcff

Tailor "Restart All Builds" for the complex realities of modern build restart rules

Summary:
Fixes T13348. Currently, the Harbormaster UI shows "Restart All Builds", but it really means "Restart Restartable Builds", which is often fewer than "All" builds (because of autobuilds, permissions, and/or configuration).

Remove the misleading term "All" and make the workflow preview exactly which builds will and will not be affected, and why.

Test Plan:
{F6636313}

{F6636314}

{F6636315}

Reviewers: amckinley…