Rename a parse node to be more general

A WHERE clause will be used for row filtering in logical replication.
We already have a similar node: 'WHERE (condition here)'.  Let's
rename the node to a generic name and use it for row filtering too.

Author: Euler Taveira <euler.taveira@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/CAHE3wggb715X+mK_DitLXF25B=jE6xyNCH4YOwM860JR7HarGQ@mail.gmail.com

src/backend/parser/gram.y

@@ -495,7 +495,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <node>	def_arg columnElem where_clause where_or_current_clause
 				a_expr b_expr c_expr AexprConst indirection_el opt_slice_bound
 				columnref in_expr having_clause func_table xmltable array_expr
-				ExclusionWhereClause operator_def_arg
+				OptWhereClause operator_def_arg
 %type <list>	rowsfrom_item rowsfrom_list opt_col_def_list
 %type <boolean> opt_ordinality
 %type <list>	ExclusionConstraintList ExclusionConstraintElem
@@ -3837,7 +3837,7 @@ ConstraintElem:
 					$$ = (Node *)n;
 				}
 			| EXCLUDE access_method_clause '(' ExclusionConstraintList ')'
-				opt_c_include opt_definition OptConsTableSpace  ExclusionWhereClause
+				opt_c_include opt_definition OptConsTableSpace  OptWhereClause
 				ConstraintAttributeSpec
 				{
 					Constraint *n = makeNode(Constraint);
@@ -3939,7 +3939,7 @@ ExclusionConstraintElem: index_elem WITH any_operator
 			}
 		;
 
-ExclusionWhereClause:
+OptWhereClause:
 			WHERE '(' a_expr ')'					{ $$ = $3; }
 			| /*EMPTY*/								{ $$ = NULL; }
 		;