ANALYZE for statements: not clear where the time is spent

ANALYZE FORMAT=JSON shows r_total_time_ms field which allows one to see where the time was spent during execution.

r_total_time_ms is provided for

• query_block, aka a SELECT
• table, individual table references
• filesort node.
• ...

The issue is that for many-table join one can frequently see that

• The join itself (query_block) took a lot of time
• table access in the join add up to a fraction of time.

this leaves one puzzled re where the time is spent.
An example of such case is MDEV-20646.