Changed|Deprecated: Deprecate use-black-ui termux property and replace it with night-mode

This will not break existing `use-black-ui` settings for users and it will automatically be converted to `night-mode` when properties are loaded from disk but a deprecation message will be logged.

This `night-mode` key can be used to set the day/night theme variant for activities used by termux app and its plugin. The user can set a string value to `true` to force use dark variant of theme, `false` to force use light variant of theme or `system` to automatically set theme based on current system settings. The default value is still `system`. The app must be restarted for changes to take effect for existing activities, including main terminal `TermuxActivity`.

This is required since "theme != night mode". In future custom theme or color support may be provided that will have both dark and night modes for the same theme.

termux-shared/src/main/java/com/termux/shared/models/theme/NightMode.java

@@ -0,0 +1,48 @@
+package com.termux.shared.models.theme;
+
+import androidx.appcompat.app.AppCompatDelegate;
+
+/** The modes used by to decide night mode for themes. */
+public enum NightMode {
+
+    /** Night theme should be enabled. */
+    TRUE("true", AppCompatDelegate.MODE_NIGHT_YES),
+
+    /** Dark theme should be enabled. */
+    FALSE("false", AppCompatDelegate.MODE_NIGHT_NO),
+
+    /**
+     * Use night or dark theme depending on system night mode.
+     * https://developer.android.com/guide/topics/resources/providing-resources#NightQualifier
+     */
+    SYSTEM("system", AppCompatDelegate.MODE_NIGHT_FOLLOW_SYSTEM);
+
+    private final String name;
+    private final int mode;
+
+    NightMode(final String name, int mode) {
+        this.name = name;
+        this.mode = mode;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public int getMode() {
+        return mode;
+    }
+
+    public static Integer modeOf(String name) {
+        if (TRUE.name.equals(name))
+            return TRUE.mode;
+        else if (FALSE.name.equals(name))
+            return FALSE.mode;
+        else if (SYSTEM.name.equals(name)) {
+            return SYSTEM.mode;
+        } else {
+            return null;
+        }
+    }
+
+}