Touch up settings: alignment, spacing, error states

Fixes https://github.com/vector-im/riot-web/issues/10554

Issues fixed:
* Fields were not ~30px from the avatar (too much right margin)
* Tooltips overflowed the dialog on some resolutions
* SetIdServer didn't have an error state for making the field red
* Spacing between sections in Discovery was wrong (fixed by just removing the problematic n+2 selector - it didn't help anything)

res/css/views/settings/_SetIdServer.scss

@@ -17,3 +17,7 @@ limitations under the License.
 .mx_SetIdServer .mx_Field_input {
     @mixin mx_Settings_fullWidthField;
 }
+
+.mx_SetIdServer_tooltip {
+    @mixin mx_Settings_tooltip;
+}