pgsql: Adjust trace_sort log messages.

Adjust trace_sort log messages.

The project message style guide dictates: "When citing the name of an
object, state what kind of object it is". The parallel CREATE INDEX
patch added a worker number to most of the trace_sort messages within
tuplesort.c without specifying the object type. Bring these messages
into compliance with the style guide.

We're still treating a leader or serial Tuplesortstate as having worker
number -1. trace_sort is a developer option, and these two cases are
highly comparable, so this seems appropriate.

Per complaint from Tom Lane.

Discussion: https://postgr.es/m/8330.1540831863@sss.pgh.pa.us
Backpatch: 11-, where parallel CREATE INDEX was introduced.

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/886319d71bd5c0ba18c9b46a1e3765d88f5ed0e7

Modified Files
--------------
src/backend/utils/sort/tuplesort.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)