Rename typedef in jsonpath_scan.l from "keyword" to "JsonPathKeyword"

Typedef name should be both unique and non-intersect with variable names
across all the sources.  That makes both pg_indent and debuggers happy.

Discussion: https://postgr.es/m/23865.1552936099%40sss.pgh.pa.us

src/backend/utils/adt/jsonpath_scan.l

@@ -282,20 +282,20 @@ jsonpath_yyerror(JsonPathParseResult **result, const char *message)
 	}
 }
 
-typedef struct keyword
+typedef struct JsonPathKeyword
 {
 	int16		len;
 	bool		lowercase;
 	int			val;
 	const char *keyword;
-} keyword;
+} JsonPathKeyword;
 
 /*
  * Array of key words should be sorted by length and then
  * alphabetical order
  */
 
-static const keyword keywords[] = {
+static const JsonPathKeyword keywords[] = {
 	{ 2, false,	IS_P,		"is"},
 	{ 2, false,	TO_P,		"to"},
 	{ 3, false,	ABS_P,		"abs"},
@@ -324,7 +324,7 @@ checkSpecialVal()
 {
 	int						res = IDENT_P;
 	int						diff;
-	const keyword  *StopLow = keywords,
+	const JsonPathKeyword  *StopLow = keywords,
 						   *StopHigh = keywords + lengthof(keywords),
 						   *StopMiddle;