Do a tiny bit of header file maintenance

Stop including utils/relcache.h in access/genam.h, and stop including
htup_details.h in nodes/tidbitmap.h.  Both these files (genam.h and
tidbitmap.h) are widely used in other header files, so it's in our best
interest that they remain as lean as reasonable.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/202509291356.o5t6ny2hoa3q@alvherre.pgsql

contrib/btree_gist/btree_bit.c

@@ -8,6 +8,7 @@
 #include "utils/fmgrprotos.h"
 #include "utils/sortsupport.h"
 #include "utils/varbit.h"
+#include "varatt.h"
 
 /* GiST support functions */
 PG_FUNCTION_INFO_V1(gbt_bit_compress);