colfetcher,row: decode only needed columns when tracing is enabled

[cockroach-teamcity]

Exalate commented:

cockroachdb/cockroach#74236 --- Release note (sql change): The KV tracing of SQL queries (that could be obtained with %5Cset auto_trace=on,kv) has been adjusted slightly. Previously, we would fully decode the key part of each key-value pair even if some part of the key would not be decoded when tracing is enabled. Now, we won't perform any extra decoding, and parts of the key that aren't decoded are replaced with ?.

Jira Issue: DOC-2270

Jira Issue: DOC-4212

[exalate-issue-sync]

Vy Ton (vy-ton) commented:
Stephanie Bodoff I don’t think this needs docs?

[exalate-issue-sync]

Stephanie Bodoff (stbof) commented:
Contents of KV pair not covered in docs.