Motivated by this comment in WT-13166.
We often cast a WT_CURSOR cursor to one of it's implementations (WT_CURSOR_HS, WT_CURSOR_BTREE, etc) with a direct cast, however we don't perform any sanity checks that we are converting to the correct type. If we convert a WT_CURSOR_HS to a WT_CURSOR_BTREE instead we'll read invalid data from the structure, or possibly data beyond the end of the struct.

This ticket is to add a new field WT_CURSOR::cursor_type to the WT_CURSOR interface so we can validate during type casting that we're casting to the correct type. This field should be HAVE_DIAGNOSTIC only and not exposed in the public API.

The end result is that existing casts

c = (WT_CURSOR_BTREE*) cursor;

will perform correctness checks

c = CUR_2_CURBT(cursor);

// A possible implementation using the comma operator
#define CUR_2_CURBT(cursor) (WT_ASSERT(cursor->cursor_type == WT_CURSOR_TYPE_BTREE), (WT_CURSOR_BTREE*) cursor)