pgsql: Rename PageData to GenericXLogPageData

Rename PageData to GenericXLogPageData

In the PostgreSQL C type naming schema, the type PageData should be
what the pointer of type Page points to.  But in this case it's
actually an unrelated type local to generic_xlog.c.  Rename that to a
more specific name.  This makes room to possible add a PageData type
with the mentioned meaning, but this is not done here.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/001d457e-c118-4219-8132-e1846c2ae3c9%40eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ddbba3aac868132137782b02a4e81218cfd3b4b9

Modified Files
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src/backend/access/transam/generic_xlog.c | 24 ++++++++++++------------
src/tools/pgindent/typedefs.list          |  2 +-
2 files changed, 13 insertions(+), 13 deletions(-)