MustNotUseCompanyMx exceptions should display error on UI

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.3.X, Master
• Fix Version/s: 7.3.X, 7.3.5 CE GA6, 7.3.10 DXP GA1, Master
• Component/s: Application Security > SAML
• Labels: None
• Branch Version/s:
  7.3.x
• Backported to Branch:
  Committed
• Fix Priority: 3
• Sprint: Iteration 46
• Git Pull Request: https://github.com/martamedio/liferay-portal/pull/184

1. Setup SP & IDP portal instances and connect them as usual
2. On the IDP, create a new user [e-mail]
3. On the SP navigate to Control Panel > Configuration > Instance Settings
4. Click User Authorization
5. Checked "Allow strangers to create accounts?" and uncheck "Allow strangers to create accounts with a company email address?". Save.
6. Navigate to SAML Admin and edit the IDP Connection. Check "Unknown Users Are Strangers". Save
7. Logout of the SP
8. Complete a SP initiated SSO via the "Sign in" link, using the [e-mail] user created in step 2

 Expected result: Toast appears stating that "email domain is reserved"
 Actual result: Toast appears stating that "email address is incomplete or invalid"