Implement default assist app setting

- Add "None" support to AppListPreference
- Add DefaultAssistPreference to manage assist;
- Add AppListPreferenceWithSettings to show a settings icon;
- Implement DefaultAssistPreference based on AppListPreferenceWithSettings;
- Move voice input settings into ManageAssist and implement it
  based on AppListPreferenceWithSettings;

Bug:20210110
Change-Id: If283b8b55a46b428ecfa6e45dc2123292b1d4302

src/com/android/settings/AppListPreferenceWithSettings.java

@@ -0,0 +1,59 @@
+package com.android.settings;
+
+import android.content.ComponentName;
+import android.content.Context;
+import android.content.Intent;
+import android.util.AttributeSet;
+import android.view.View;
+import android.view.ViewGroup;
+
+/**
+ * An AppListPreference with optional settings button.
+ */
+public class AppListPreferenceWithSettings extends AppListPreference {
+
+    private View mSettingsIcon;
+    private ComponentName mSettingsComponent;
+
+    public AppListPreferenceWithSettings(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        setWidgetLayoutResource(R.layout.preference_widget_settings);
+    }
+
+    @Override
+    protected void onBindView(View view) {
+        super.onBindView(view);
+
+        mSettingsIcon = view.findViewById(R.id.settings_button);
+        mSettingsIcon.setOnClickListener(new View.OnClickListener() {
+            @Override
+            public void onClick(View v) {
+                Intent intent = new Intent(Intent.ACTION_MAIN);
+                intent.setComponent(mSettingsComponent);
+                getContext().startActivity(new Intent(intent));
+            }
+        });
+
+        ViewGroup container = (ViewGroup) mSettingsIcon.getParent();
+        container.setPaddingRelative(0, 0, 0, 0);
+
+        updateSettingsVisibility();
+    }
+
+    private void updateSettingsVisibility() {
+        if (mSettingsIcon == null) {
+            return;
+        }
+
+        if (mSettingsComponent == null) {
+            mSettingsIcon.setVisibility(View.GONE);
+        } else {
+            mSettingsIcon.setVisibility(View.VISIBLE);
+        }
+    }
+
+    protected void setSettingsComponent(ComponentName settings) {
+        mSettingsComponent = settings;
+        updateSettingsVisibility();
+    }
+}