fix(material/select): ensure arrow is centered on all densities

On lower densities some form field appearances hide the label which caused the arrow to be misaligned. These changes add an override to center the label again.

Fixes #26757.

Author: crisbeto

src/material/select/_select-theme.scss

@@ -2,6 +2,8 @@
 @use '@material/menu-surface' as mdc-menu-surface;
 @use '@material/list/evolution-mixins' as mdc-list;
 @use '@material/typography' as mdc-typography;
+@use '@material/density' as mdc-density;
+@use '@material/textfield' as mdc-textfield;
 
 @use '../core/theming/theming';
 @use '../core/typography/typography';
@@ -79,7 +81,24 @@
   }
 }
 
-@mixin density($config-or-theme) {}
+@mixin density($config-or-theme) {
+  $density-scale: theming.get-density-config($config-or-theme);
+
+  // Density is clamped at -5 here, because MDC's form field throws an error for anything lower.
+  $form-field-height: mdc-density.prop-value(
+    $density-config: mdc-textfield.$density-config,
+    $density-scale: theming.clamp-density($density-scale, -5),
+    $property-name: height,
+  );
+
+  // On lower densities the filled form field hides its label which causes the label to
+  // be misaligned. Remove the additional offset that was added because of the label.
+  @if ($form-field-height < mdc-textfield.$minimum-height-for-filled-label) {
+    .mat-form-field-appearance-fill .mat-mdc-select-arrow-wrapper {
+      transform: none;
+    }
+  }
+}
 
 @mixin theme($theme-or-color-config) {
   $theme: theming.private-legacy-get-theme($theme-or-color-config);