[WebAuthn] Introduce ChangePinController

ChangePinController signals if the user can change a PIN. And if so,
it can start the flow.
The controller will be wired to PasswordsPrivate APIs and will be used
in the settings UI.

I hope to add unit tests separately -unfortunately the EnclaveManager
is not mockable yet.

Bug: 331611435
Change-Id: Ib62b042fdac3ad70d23ec7bab1e51e67298ccce4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5412493


Commit-Queue: Adem Derinel <derinel@google.com>
Reviewed-by: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282331}