add some supported columns for STATISTICS and COLUMNS info schema tables

[jennifersp]

• Added sub_part for STATISTICS table.
• Fixed column_default, datetime_precision, extra and other columns for COLUMNS table.
• Skipped cardinality column for STATISTICS table as it's not supported in Dolt yet.
• Skipped privileges column for COLUMNS table for now. (in progress)
• Modified all Dolt supported MySQL functions to use its FunctionName() method to create the string statement of the function itself. The FunctionName() method returns the name of the function in all lower cases. This makes it so that all Dolt supported MySQL functions are consistent to what MySQL returns for queries such as SHOW CREATE TABLE or the column_default of information_schema.COLUMNS table.

Notes:

• Dolt does not support Time length yet.
• Dolt currently handles BOOL and TINYINT data types the same with INT8, but MySQL explicitly defines BOOL as tinyint(1), which is different from tinyint for TINYINT data types.
• View columns are not available in COLUMNS table yet.

[fulghum]

Lots of nice changes in here @jennifersp! Keep 'em coming! 🚢