refactor: Add dedicated whitespace module

[ngeor]

• Removed obsolete TODOs
• Moved whitespace related parsers to a new module whitespace under pc_specific.
• Removed the PaddedByWs trait, replaced it with a function
• Removed the unused whitespace function
• Added lead_ws and lead_opt_ws functions
• use lead_ws in a few cases
• use lead_ws in a few cases
• use lead_ws and lead_opt_ws a bit more
• Adding demand_ws and demand_lead_ws functions
• Added function demand_lead_ws_ctx to deal with SetContext being a different trait
• Removed opt_and_keep_right
• Removed opt_and
• Created dedicated parser IgnoringParser for skipping whitespace
• Revert "Created dedicated parser IgnoringParser for skipping whitespace"
• fix build after rebase