Refactor option handling of CLUSTER, REINDEX and VACUUM

This continues the work done in b5913f6.  All the options of those
commands are changed to use hex values rather than enums to reduce the
risk of compatibility bugs when introducing new options.  Each option
set is moved into a new structure that can be extended with more
non-boolean options (this was already the case of VACUUM).  The code of
REINDEX is restructured so as manual REINDEX commands go through a
single routine from utility.c, like VACUUM, to ease the allocation
handling of option parameters when a command needs to go through
multiple transactions.

This can be used as a base infrastructure for future patches related to
those commands, including reindex filtering and tablespace support.

Per discussion with people mentioned below, as well as Alvaro Herrera
and Peter Eisentraut.

Author: Michael Paquier, Justin Pryzby
Reviewed-by: Alexey Kondratov, Justin Pryzby
Discussion: https://postgr.es/m/X8riynBLwxAD9uKk@paquier.xyz

src/include/commands/defrem.h

@@ -34,11 +34,7 @@ extern ObjectAddress DefineIndex(Oid relationId,
 								 bool check_not_in_use,
 								 bool skip_build,
 								 bool quiet);
-extern int	ReindexParseOptions(ParseState *pstate, ReindexStmt *stmt);
-extern void ReindexIndex(RangeVar *indexRelation, int options, bool isTopLevel);
-extern Oid	ReindexTable(RangeVar *relation, int options, bool isTopLevel);
-extern void ReindexMultipleTables(const char *objectName, ReindexObjectType objectKind,
-								  int options);
+extern void ExecReindex(ParseState *pstate, ReindexStmt *stmt, bool isTopLevel);
 extern char *makeObjectName(const char *name1, const char *name2,
 							const char *label);
 extern char *ChooseRelationName(const char *name1, const char *name2,