puzzles: resync with Simon's upstream e00cb46 from 25 Sep 2025.

Notably, this enables "Group".

This also includes some changes to the Rockbox frontend:

- Removes extraneous underline from Extensive Help text.

- Implements a workaround for an upstream breaking change that removes
  the BLITTER_FROMSAVED flag. We depend on this for mouse mode. This
  is apparently the only place this flag was ever used. Note that I've
  hardcoded an arbitrary negative value for BLITTER_FROMSAVED instead
  of -1, for the reason Ben Harris mentioned in his commit removing it
  from the upstream source tree.

- Adds an implicit clip() to the game region when drawing a
  puzzle. This fixes a bug in Untangle where dragging a point off
  screen leads to ugly lines outside the play area.

- Implements "Quick Help" for unfinished plugins (but not "Extensive
  Help").

- Documents the need to disable unfinished plugins in resync.sh (weak
  symbols on win32).

Change-Id: Ic318a5db4b15acb437a3f951fbc9b7919c6fa652

apps/plugins/puzzles/help.h

@@ -4,7 +4,9 @@
 #include "lib/display_text.h"
 #endif
 
-/* defined in help/ */
+/* Normally, these are defined in help/*.c. If the game lacks help
+ * text (i.e. it is an unfinished game), there are weak dummy
+ * definitions in dummy/nullhelp.c. */
 extern const char help_text[];
 #if defined(ROCKBOX) || defined(LZ4TINY)
 extern const char quick_help_text[];
@@ -15,4 +17,4 @@ extern const unsigned short help_text_len, quick_help_text_len, help_text_words;
 extern struct style_text help_text_style[];
 #endif
 
-extern const bool help_valid;
+extern const bool help_text_valid, quick_help_valid;