Fix shadow warnings in logical replication code

The -Wshadow compiler option reported 3 shadow warnings within the
logical replication files. (These are all in old code)

PSA a patch to address those.

======

logicalfuncs.c:184:13: warning: declaration of ‘name’ shadows a
previous local [-Wshadow]
char *name = TextDatumGetCString(datum_opts[i]);
^
logicalfuncs.c:105:8: warning: shadowed declaration is here [-Wshadow]
Name name;
^

~~~

reorderbuffer.c:4843:10: warning: declaration of ‘isnull’ shadows a
previous local [-Wshadow]
bool isnull;
^
reorderbuffer.c:4734:11: warning: shadowed declaration is here [-Wshadow]
bool *isnull;
^

~~~

walsender.c:3543:14: warning: declaration of ‘sentPtr’ shadows a
global declaration [-Wshadow]
XLogRecPtr sentPtr;
^
walsender.c:155:19: warning: shadowed declaration is here [-Wshadow]
static XLogRecPtr sentPtr = InvalidXLogRecPtr;
^

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Kind Regards,
Peter Smith.
Fujitsu Australia