Split CollateClause into separate raw and analyzed node types.

CollateClause is now used only in raw grammar output, and CollateExpr after
parse analysis.  This is for clarity and to avoid carrying collation names
in post-analysis parse trees: that's both wasteful and possibly misleading,
since the collation's name could be changed while the parsetree still
exists.

Also, clean up assorted infelicities and omissions in processing of the
node type.

src/include/nodes/parsenodes.h

@@ -265,6 +265,17 @@ typedef struct TypeCast
 	int			location;		/* token location, or -1 if unknown */
 } TypeCast;
 
+/*
+ * CollateClause - a COLLATE expression
+ */
+typedef struct CollateClause
+{
+	NodeTag		type;
+	Node	   *arg;			/* input expression */
+	List	   *collname;		/* possibly-qualified collation name */
+	int			location;		/* token location, or -1 if unknown */
+} CollateClause;
+
 /*
  * FuncCall - a function or aggregate invocation
  *