pgsql: Improve jumble squashing through CoerceViaIO and RelabelType

Improve jumble squashing through CoerceViaIO and RelabelType

There's no principled reason for query jumbling to only remove the first
layer of RelabelType and CoerceViaIO.  Change it to see through as many
layers as there are.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/debad29d22152d7fe4c4e671090e20238647c460

Modified Files
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contrib/pg_stat_statements/expected/squashing.out | 40 ++++++++++++++---------
contrib/pg_stat_statements/sql/squashing.sql      |  9 ++---
src/backend/nodes/queryjumblefuncs.c              | 27 ++++++++-------
3 files changed, 45 insertions(+), 31 deletions(-)