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/slide.c

@@ -0,0 +1,2 @@
+const char quick_help_text[] = "Slide the blocks to let the key block out.";
+const bool quick_help_valid = true;