feat(auto): equalizer folder in the browse tree, one toggle on playback

On-device feedback: two identical icons on the car's now-playing screen,
one of which looked dead. It worked -- but head units render custom
actions icon-first, so cycling six presets behind one static glyph was
invisible.

A monochrome icon cannot encode which of six presets is active. Android
Auto separates the idioms deliberately: custom actions for stateless
toggles, browsable lists for choosing among options.

- Playback screen keeps one action: equalizer on/off, state-aware icons
- New Ecualizador folder lists Desactivar plus the six presets by name,
  active one marked
- The preset-cycling action and its drawable are removed

Supersedes the redesign's no-equalizer-folder rule, which predated
knowing custom actions do not surface state in a car.

# Conflicts:
#	lib/l10n/app_ar.arb
#	lib/l10n/app_bn.arb
#	lib/l10n/app_de.arb
#	lib/l10n/app_en.arb
#	lib/l10n/app_es.arb
#	lib/l10n/app_fr.arb
#	lib/l10n/app_hi.arb
#	lib/l10n/app_id.arb
#	lib/l10n/app_it.arb
#	lib/l10n/app_ja.arb
#	lib/l10n/app_pt.arb
#	lib/l10n/app_ru.arb
#	lib/l10n/app_zh.arb

lib/l10n/gen/app_localizations.dart

@@ -3187,6 +3187,12 @@ abstract class AppLocalizations {
   /// In es, this message translates to:
   /// **'Todavía no pudimos revisar tus ajustes de alarma.'**
   String get alarmDiagnosticsUnavailableHint;
+
+  /// No description provided for @autoEqDisableOption.
+  ///
+  /// In es, this message translates to:
+  /// **'Desactivar'**
+  String get autoEqDisableOption;
 }
 
 class _AppLocalizationsDelegate