Support `toolkit-theme-set-functions' on Android and execute hooks safely

* java/org/gnu/emacs/EmacsNative.java (setEmacsParams): New arg
UIMODE.
(sendConfigurationChanged): New args DETAIL and UI_MODE.

* java/org/gnu/emacs/EmacsNoninteractive.java (main1): Provide
an undefined UI mode.

* java/org/gnu/emacs/EmacsService.java (EmacsService): New field
uiMode.
(onCreate): Initialize this field at start-up and provide the
same to setEmacsParams.
(onConfigurationChanged): If the UI mode has been altered,
generate a configuration changed event to match.

* src/android.c (android_ui_mode): New variable.
(setEmacsParams): New argument UI_MODE.  Initialize the same
from this variable.

* src/androidgui.h (enum android_configuration_changed): New
enum.
(struct android_configuration_changed_event): New field
`DETAIL'.  Convert fields providing specifics into a union of
display density information and a UI mode integer.

* src/androidterm.c (handle_one_android_event): Handle both
manners of configuration change events.
(android_term_init): Initialize Vtoolkit_theme from UI mode
provided at start-up.

* src/frame.c (syms_of_frame): Always define Vtoolkit_theme.
Define Qtoolkit_theme_set_functions.

* src/gtkutil.c (xg_update_dark_mode_for_all_displays):

* src/w32term.c (w32_read_socket): Generate special toolkit
theme events, rather than executing hooks directly within the
read_socket callback.

* src/keyboard.c (kbd_buffer_get_event)
<TOOLKIT_THEME_CHANGED_EVENT>: Run Qtoolkit_theme_set_functions
and set Vtoolkit_theme from event->ie.arg.

* src/termhooks.h (enum event_kind): New event
TOOLKIT_THEME_CHANGED_EVENT.

java/org/gnu/emacs/EmacsNative.java

@@ -61,6 +61,9 @@ public final class EmacsNative
      scaledDensity is the DPI value used to translate point sizes to
      pixel sizes when loading fonts.
 
+     uiMode holds the bits of the system's UI mode specification
+     defining the active system theme.
+
      classPath must be the classpath of this app_process process, or
      NULL.
 
@@ -74,6 +77,7 @@ public final class EmacsNative
 					    float pixelDensityX,
 					    float pixelDensityY,
 					    float scaledDensity,
+					    int uiMode,
 					    String classPath,
 					    EmacsService emacsService,
 					    int apiLevel);
@@ -197,8 +201,9 @@ public final class EmacsNative
   public static native void sendNotificationAction (String tag, String action);
 
   /* Send an ANDROID_CONFIGURATION_CHANGED event.  */
-  public static native void sendConfigurationChanged (float dpiX, float dpiY,
-						      float dpiScaled);
+  public static native void sendConfigurationChanged (int detail, float dpiX,
+						      float dpiY, float dpiScaled,
+						      int ui_mode);
 
   /* Return the file name associated with the specified file
      descriptor, or NULL if there is none.  */