Fix T83886: Particle instance modifier broken

Caused by Caused by rB83980506957c.

Since above commit, the modifier was created with wrong initial values
[amount was 0.0 and offset was 1.0 -- instead of the other way around].

Since there is no way to fix existing files in a reasonable way I guess,
all we can do here is to make sure that from now on, the defaults are
correct.

Maniphest Tasks: T83886

Differential Revision: https://developer.blender.org/D9881

source/blender/makesdna/DNA_modifier_defaults.h

@@ -503,8 +503,8 @@
     .random_position = 0.0f, \
     .rotation = 0.0f, \
     .random_rotation = 0.0f, \
-    .particle_offset = 1.0f, \
-    .particle_amount = 0.0f, \
+    .particle_offset = 0.0f, \
+    .particle_amount = 1.0f, \
     .index_layer_name = "", \
     .value_layer_name = "", \
   }