pgsql: Rename pg_verifybackup's JsonManifestParseContext callback funct

Rename pg_verifybackup's JsonManifestParseContext callback functions.

The old names were too generic, and would have applied to any binary
that made use of JsonManifestParseContext. Rename to make the names
specific to pg_verifybackup, since there are plans afoot to reuse
this infrastructure.

Per suggestion from Álvaro Herrra.

Discussion: http://postgr.es/m/202311131625.o7hzq3oukuyd@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/278eb13c48236c261ed4bab1cb4696321e346eb7

Modified Files
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src/bin/pg_verifybackup/pg_verifybackup.c | 36 +++++++++++++++----------------
1 file changed, 18 insertions(+), 18 deletions(-)