pgsql: Revert "Remove fake FunctionCallInfos from the stats .."

Revert "Remove fake FunctionCallInfos from the stats .."

This reverts commit cc9a8eb112fa, after more discussion with Etsuro
Fujita. We are still not sure about the interface that should be used
for the portion related to the statistics import, and what should be
exposed for FDW code that may want to rely on these two functions:
- import_attribute_statistics()
- import_relation_statistics()

Discussion: https://postgr.es/m/CAPmGK15HUuNvEZk4b+K_x57+sg31B9LDwB7DBgVNaCpLnafhPA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6fe9b62914bcb55cbf02d8d741a42f810d239725

Modified Files
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contrib/postgres_fdw/postgres_fdw.c | 69 ++++-----
src/backend/statistics/attribute_stats.c | 215 +++++++++++++++-----------
src/backend/statistics/extended_stats_funcs.c | 81 +++++-----
src/backend/statistics/relation_stats.c | 127 ++++++++-------
src/backend/statistics/stat_utils.c | 56 +++----
src/include/statistics/stat_utils.h | 19 ++-
src/include/statistics/statistics.h | 66 +++-----
src/tools/pgindent/typedefs.list | 2 -
8 files changed, 335 insertions(+), 300 deletions(-)