Tiered storage now has "tiered:" dhandles and uris that behave like Btrees, but are allowed to span multiple files. There are lots of places in the code that asks "is this dhandle a btree?". Rather than compare dhandle->type to WT_DHANDLE_TYPE_BTREE, we should use a macro.
This issue is related to WT-7518, but is a simpler approach in that there are no changes to data structures.