Re: Make COPY format extendable: Extract COPY TO format implementations

I ran `make headerscheck` after these patches and it reported a few
problems:

/pgsql/source/master/src/tools/pginclude/headerscheck /pgsql/source/master /pgsql/build/master
In file included from /tmp/headerscheck.xdG40Y/test.c:2:
/pgsql/source/master/src/include/commands/copyapi.h:76:44: error: unknown type name ‘CopyFromState’; did you mean ‘CopyToState’?
76 | void (*CopyFromInFunc) (CopyFromState cstate, Oid atttypid,
| ^~~~~~~~~~~~~
| CopyToState
/pgsql/source/master/src/include/commands/copyapi.h:87:43: error: unknown type name ‘CopyFromState’; did you mean ‘CopyToState’?
87 | void (*CopyFromStart) (CopyFromState cstate, TupleDesc tupDesc);
| ^~~~~~~~~~~~~
| CopyToState
/pgsql/source/master/src/include/commands/copyapi.h:98:44: error: unknown type name ‘CopyFromState’; did you mean ‘CopyToState’?
98 | bool (*CopyFromOneRow) (CopyFromState cstate, ExprContext *econtext,
| ^~~~~~~~~~~~~
| CopyToState
/pgsql/source/master/src/include/commands/copyapi.h:102:41: error: unknown type name ‘CopyFromState’; did you mean ‘CopyToState’?
102 | void (*CopyFromEnd) (CopyFromState cstate);
| ^~~~~~~~~~~~~
| CopyToState
/pgsql/source/master/src/include/commands/copyapi.h:103:1: warning: no semicolon at end of struct or union
103 | } CopyFromRoutine;
| ^

I think the fix should be the attached.

--
Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
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