pgsql: Use PG_GETARG_TRANSACTIONID where appropriate

Use PG_GETARG_TRANSACTIONID where appropriate

Some places were using PG_GETARG_UINT32 where PG_GETARG_TRANSACTIONID
would be more appropriate. (Of course, they are the same internally,
so there is no externally visible effect.) To do that, export
PG_GETARG_TRANSACTIONID outside of xid.c. We also export
PG_RETURN_TRANSACTIONID for symmetry, even though there are currently
no external users.

Author: Ashutosh Bapat <ashutosh(dot)bapat(at)2ndquadrant(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/d8f6bdd536df403b9b33816e9f7e0b9d(at)G08CNEXMBPEKD05(dot)g08(dot)fujitsu(dot)local

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/dd26a0ad760b11237d7ea9cda8ccccc1826c2c64

Modified Files
--------------
src/backend/access/transam/commit_ts.c | 4 ++--
src/backend/access/transam/multixact.c | 2 +-
src/backend/utils/adt/xid.c | 3 ---
src/include/fmgr.h | 2 ++
4 files changed, 5 insertions(+), 6 deletions(-)