Disable autocorrect and autocaptialisation when entering username for SSO registration. (#13350)

When registering a new account via SSO on iOS, the text field becomes pretty annoying as it autocapitalises and autocorrects your input. This PR fixes that (although I have only tested the raw HTML file on the simulator, I'm not sure how to get the complete setup available for testing in the flow).

Author: pixlwave

changelog.d/13350.bugfix

@@ -0,0 +1 @@
+Disable autocorrection and autocapitalisation on the username text field shown during registration when using SSO.

synapse/res/templates/sso_auth_account_details.html

@@ -138,7 +138,7 @@ <h1>Create your account</h1>
         <div class="username_input" id="username_input">
           <label for="field-username">Username (required)</label>
           <div class="prefix">@</div>
-          <input type="text" name="username" id="field-username" value="{{ user_attributes.localpart }}" autofocus>
+          <input type="text" name="username" id="field-username" value="{{ user_attributes.localpart }}" autofocus autocorrect="off" autocapitalize="none">
           <div class="postfix">:{{ server_name }}</div>
         </div>
         <output for="username_input" id="field-username-output"></output>