- ASTManager helper class to hold the top node of the ast to be printed
- HDoParseRetBreakpoint
- ast printing commands
- Update BreakpointManager tests with HDoParseRetBreakpoint tests
- Add support in TopLevelParse to select a stack item for printing the AST node of

Fix breakpoint_manager not using its own retq finding function

Finally, instead of having to hardcode a constant, the length of
the code to disassemble in search of a RET instruction is discovered
at runtime.

Also update PDFMainBreakpoint after moving set_hammer_retq_breakpoints() to BreakpointManager