pgsql: Refactor code retrieving string for RecoveryPauseState

Refactor code retrieving string for RecoveryPauseState

This refactoring is going to be useful in an upcoming commit, to avoid
some code duplication with the function pg_get_wal_replay_pause_state(),
that returns a string for the recovery pause state.

Refactoring opportunity noticed while hacking on a different patch.

Discussion: https://postgr.es/m/CABPTF7W+Nody-+P9y4PNk37-QWuLpfUrEonHuEhrX+Vx9Kq+Kw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/42a12856a6a09e6477a8e9156cfa39cc3a8708e0

Modified Files
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src/backend/access/transam/xlogfuncs.c | 47 ++++++++++++++++++++++------------
1 file changed, 31 insertions(+), 16 deletions(-)