[ticket/12213] Add MCP events for custom quick moderation options

Add core events to mcp.php and mcp_main.php. This allows
extensions to add and to handle custom quick moderation options.

PHPBB3-12213
[ticket/12190] Add core event "core.modify_submit_post_data"
Add core event - core.modify_submit_post_data
to submit_post() function. This allows extensions to modify the
whole post data before the post submitting, or even provide
its own post submit procedure.

PHPBB3-12190