Verify WipeTower Footprint at Point of Generation

The clamps and validation work from estimates. Once the tower is
generated, _make_wipe_tower re-tests the exact first-layer footprint,
brim and cone base included, against the printable area and the
exclusion zone, so an off-plate tower fails with a clear error instead
of exporting unprintable G-code. The rectangle-wall mesh footprint
learns the Type2 cone base so that check and the post-generation
validation see the real outline.

Pre-generation, validation hard-checks the body plus an explicit brim
and warns on the estimated auto brim and cone base with the existing
"may collide" strings, so the user hears about a marginal position on
the first slice rather than only at generation time.

Two fff_print fixtures that print a tower at the default position move
it onto the 200 mm test bed, as the multifilament fixtures already do:
the shipped default y of 220 is off that bed, and the backstop now says
so instead of exporting the tower.

tests/fff_print/test_wipe_tower.cpp

@@ -152,6 +152,8 @@ static DynamicPrintConfig wipe_tower_toolchange_config(const std::string &gcode_
         { "outer_wall_filament_id",     2 },
         { "inner_wall_filament_id",     2 },
         { "enable_prime_tower",         true },
+        { "wipe_tower_x",               50 }, // inside the 200x200 test bed
+        { "wipe_tower_y",               50 }, // (the default y, 220, is not)
         { "layer_height",               0.3 },
         { "gcode_flavor",               gcode_flavor },
     });