Accessibility testing for the Blazor Web template

[mkArtakMSFT]

After we're done with the Blazor Web project template restructuring work #49412, and the Blazor Web Identity UI work in RC1, we need to run the accessibility insights over the new template and address all the issues.

[mkArtakMSFT]

This will need to be exuected after #48786 is complete.

[MackinnonBuck]

We fixed multiple accessibility issues in #50722, each of them relating to Identity UI:

• Multiple elements on the page with the same ID ("email")
• Color contrast issues:
  • External login page info text had insufficient contrast with the background
  • Link colors had insufficient contrast with the info alert background
  • Validation messages had insufficient contrast with the background
• An aria role issue where <ul> elements had the "alert" role (removed the "role" attribute from each <ul>)
• An invalid value for the autocomplete attribute (was "confirm-password", changed to "new-password").