WL#8063: True bottom-up server parser: refactoring of the LOAD statement

Affects: Server-8.0   —   Status: Complete   —   Priority: Medium

This WL is intended to refactor LOAD DATA/XML statement grammar rules in a pure bottom-up style to make it context-independent for the better maintainability and extendibility.
Functional requirements


Non-functional requirements

NF-1: No performance degradation is expected.
User Documentation

No user-visible changes. No documentation required. 
New classes

Class name   | Description
PT_load      | Parse tree root for `LOAD DATA/XML`
Sql_cmd_load | Command class for `LOAD DATA/XML`

Removal of unneeded "global" variables

* LEX::exchange
* LEX::load_field_list
* LEX::load_update_list
* LEX::load_value_list
* LEX::load_set_str_list
* LEX::local_file