pgsql: Move planner row-estimation tests to new planner_est.sql

Move planner row-estimation tests to new planner_est.sql

Move explain_mask_costs() and the associated planner row-estimation
tests from misc_functions.sql to a new regression test file,
planner_est.sql.

Previously, there wasn't an ideal home for such tests, likely as there
were very few such tests due to width and selectivity estimations being
too dependent on statistics and hardware. That's not always the case, as
we have SupportRequestRows support functions. More such tests are
possibly on the way, so let's create a better home so that we don't have
to create the explain_mask_costs() function in each file we might have
added such tests to.

Author: Ilia Evdokimov <ilya(dot)evdokimov(at)tantorlabs(dot)com>
Reviewed-by: David Rowley <dgrowleyml(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAApHDvphShGABn-3AoE36dTvGHW7gUpFSw0_ZZnH84wGCW3hHw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/374a6394c6ae2e6f8b70ca7897e1499ff72ae7e5

Modified Files
--------------
src/test/regress/expected/misc_functions.out | 178 -------------------------
src/test/regress/expected/planner_est.out | 186 +++++++++++++++++++++++++++
src/test/regress/parallel_schedule | 2 +-
src/test/regress/sql/misc_functions.sql | 125 ------------------
src/test/regress/sql/planner_est.sql | 135 +++++++++++++++++++
5 files changed, 322 insertions(+), 304 deletions(-)