fix: idp user information mapping (#9892)

# Which Problems Are Solved

When retrieving the information of an IdP intent, depending on the IdP
type (e.g. Apple), there was issue when mapping the stored (event)
information back to the specific IdP type, potentially leading to a
panic.

# How the Problems Are Solved

- Correctly initialize the user struct to map the information to.

# Additional Changes

none

# Additional Context

- reported by a support request
- needs backport to 3.x and 2.x

(cherry picked from commit 1b2fd23e0b)

internal/idp/providers/google/google.go

@@ -34,6 +34,10 @@ var userMapper = func(info *openid.UserInfo) idp.User {
 	return &User{oidc.DefaultMapper(info)}
 }
 
+func InitUser() idp.User {
+	return &User{oidc.InitUser()}
+}
+
 // User is a representation of the authenticated Google and implements the [idp.User] interface
 // by wrapping an [idp.User] (implemented by [oidc.User]). It overwrites the [GetPreferredUsername] to use the `email` claim.
 type User struct {