pgsql: Invent struct ReindexIndexInfo

Invent struct ReindexIndexInfo

This struct is used by ReindexRelationConcurrently to keep track of the
relations to process.  This saves having to obtain some data repeatedly,
and has future uses as well.

Reviewed-by: Dmitry Dolgov <9erthalion6@gmail.com>
Reviewed-by: Hamid Akhtar <hamid.akhtar@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/20201130195439.GA24598@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c6c4b37395b22f7e649234453a0aafe74d61b7e6

Modified Files
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src/backend/commands/indexcmds.c | 126 ++++++++++++++++++++-------------------
src/tools/pgindent/typedefs.list |   1 +
2 files changed, 66 insertions(+), 61 deletions(-)