Ignore BRIN indexes when checking for HOT udpates

Ignore BRIN indexes when checking for HOT udpates

When determining whether an index update may be skipped by using HOT, we
can ignore attributes indexed only by BRIN indexes. There are no index
pointers to individual tuples in BRIN, and the page range summary will
be updated anyway as it relies on visibility info.

This also removes rd_indexattr list, and replaces it with rd_attrsvalid
flag. The list was not used anywhere, and a simple flag is sufficient.

Patch by Josef Simanek, various fixes and improvements by me.

Author: Josef Simanek
Reviewed-by: Tomas Vondra, Alvaro Herrera
Discussion: https://postgr.es/m/CAFp7QwpMRGcDAQumN7onN9HjrJ3u4X3ZRXdGFT0K5G2JWvnbWg%40mail.gmail.com