Derive PAS_MAX_OBJECTS_PER_PAGE from small page size

The previous hardcoded 2048 assumed PAS_SMALL_PAGE_DEFAULT_SIZE=16KB.
With 64KB pages, num_alloc_bits = page_size >> min_align_shift can reach
8192 (utility heap, PAS_INTERNAL_MIN_ALIGN_SHIFT=3), causing
pas_baseline_allocator_attach_directory to PAS_ASSERT when a thread hits
the baseline allocator slow path.

Author: dylan-conway

Source/bmalloc/libpas/src/libpas/pas_internal_config.h

@@ -152,7 +152,9 @@
 
 #define PAS_NUM_BASELINE_ALLOCATORS      32u
 
-#define PAS_MAX_OBJECTS_PER_PAGE         2048
+/* Must be >= max(page_size >> min_align_shift) across all segregated configs.
+   Utility heap uses PAS_INTERNAL_MIN_ALIGN_SHIFT (3) with the small page. */
+#define PAS_MAX_OBJECTS_PER_PAGE         (PAS_SMALL_PAGE_DEFAULT_SIZE >> PAS_INTERNAL_MIN_ALIGN_SHIFT)
 
 #define PAS_MPROTECT_DECOMMITTED         PAS_ENABLE_TESTING