Optimizer trace support for different parts of the server

This task is for checking how optimizer trace uses different parts of the server.

Done:

• Condition transformation (DONE)
• KEYUSE objects (DONE)
• Range access (DONE)

Not yet handled:

• EITS: condition selectivities computed for each table (TODO, see below)
• "Late" ORDER BY optimization (less-defined TODO, see some notes below)
• Join optimization tracing (TODO: how to do it?)
• Derived table merging
• Conversion of subqueries into semi-joins
• Table elimination