Refactor SQLLogicTest

[Mytherin]

This PR refactors and cleans up the SQLLogicTest framework by splitting it up into multiple files and making the code actually consistent with the rest of the project. In total the changes are as follows:

• The test runner is partitioned into different components (SQLLogicTestRunner, Command, TestParser, TestResultHelper) that are placed in separate files.
• Rewrite the test parser to be proper C++
• Rename functions and variables to be consistent with the remainder of the project
• Use classes (yay) so we can avoid having function calls with many parameters