pgsql: doc: Update pg_stat_statements about query ID calculation of uti

doc: Update pg_stat_statements about query ID calculation of utilities

Since 3db72eb, the calculation of the query ID hash for utilities is not
done based on the textual query strings, but on their internal Query
representation, meaning that there can be an overlap when they use
literal constants.  The documentation of pg_stat_statements was missing
a refresh about that.

Extracted from a larger patch by me.

Discussion: https://postgr.es/m/Y+MRdEq9W9XVa2AB@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6a88a058614bc921d6cab1cc50330ddee283c810

Modified Files
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doc/src/sgml/pgstatstatements.sgml | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)