Render underlines and tooltips on custom server names in auth pages

See https://github.com/vector-im/riot-web/issues/9290

src/components/views/auth/PasswordLogin.js

@@ -279,9 +279,16 @@ export default class PasswordLogin extends React.Component {
             serverName: this.props.serverConfig.hsName,
         });
         if (this.props.serverConfig.hsNameIsDifferent) {
-            // TODO: TravisR - Use tooltip to underline
+            const TextWithTooltip = sdk.getComponent("elements.TextWithTooltip");
+
             signInToText = _t('Sign in to your Matrix account on <underlinedServerName />', {}, {
-                'underlinedServerName': () => <u>{this.props.serverConfig.hsName}</u>,
+                'underlinedServerName': () => {
+                    return <TextWithTooltip
+                               class="mx_Login_underlinedServerName"
+                               tooltip={this.props.serverConfig.hsUrl}>
+                        {this.props.serverConfig.hsName}
+                    </TextWithTooltip>;
+                },
             });
         }