Implement Tier 1 deep parsers for EXPLAIN, CALL, DO, LOAD DATA

- parse_explain(): handles EXPLAIN [ANALYZE] [FORMAT=...] inner_stmt,
  EXPLAIN table_name (MySQL shorthand), DESCRIBE/DESC table [col],
  and PostgreSQL parenthesized options (ANALYZE, VERBOSE, FORMAT, etc.)
- parse_call(): handles CALL [schema.]proc(args...) for both dialects
- parse_do(): handles DO expr [, expr ...] (MySQL)
- parse_load_data(): handles LOAD DATA [LOCAL] INFILE '...'
  [REPLACE|IGNORE] INTO TABLE t [FIELDS TERMINATED BY ...] etc.
- Removes extract_load() (replaced by parse_load_data)
- Wires all four into classify_and_dispatch()

Author: renecannao

include/sql_parser/parser.h

@@ -57,6 +57,10 @@ class Parser {
     ParseResult parse_insert(bool is_replace = false);
     ParseResult parse_update();
     ParseResult parse_delete();
+    ParseResult parse_explain(bool is_describe = false);
+    ParseResult parse_call();
+    ParseResult parse_do();
+    ParseResult parse_load_data();
 
     // Tier 2 extractors
     ParseResult extract_insert(const Token& first);
@@ -72,7 +76,7 @@ class Parser {
     ParseResult extract_ddl(const Token& first);
     ParseResult extract_acl(const Token& first);
     ParseResult extract_lock(const Token& first);
-    ParseResult extract_load(const Token& first);
+    // extract_load removed -- replaced by parse_load_data()
     ParseResult extract_reset(const Token& first);
     ParseResult extract_unknown(const Token& first);