Remove some mcompat from elsewhere in types

This is the converse of the previous branch. It deals with references to MCOMPAT types from common functions. In most cases, that is done by splitting off a stub to instantiate with specific MySQL types. But in a couple cases (IFNULL and the CURRENT_xxx) functions, the whole thing just moves to MCOMPAT because it's a mix of MySQL specific stuff and potentially generic stuff. The implication of that is that a new bundle will either need some refactoring of those classes or to repeat some of their structure.

Similarly, TParsers gets moved to mcompat and AkBool pulled out. Here again, these parsers are somewhat MySQL specific and somewhat generic.