Allow U2F devices to be used in Firefox

What does this MR do?

• Adds U2F support for Firefox
• Improve U2F feature detection logic
• Have authentication flow be closer to the spec (single challenge instead of a challenge for each signRequest)

What are the relevant issue numbers?

• Closes #17341 (closed)
• Related to #15337 (moved)

Tasks

• #17341 (closed) !5177 (merged) Firefox support for U2F
  • Implementation
  • Tests
  • Wait for build to pass
  • Assign to endboss
  • Wait for review/merge