Add first version of DebugInfo object

[guillep]

This PR introduces an object encapsulating the debugging API of methods/contexts: DebugInfo.
This object, used in tools such as debugger, inspector, is responsible of reading variables from a context, and to obtain bytecode to source code mappings:

• is the current PC a send?
• is the current PC a store?
  ...

Particular care is taken for optimized/inlined contexts, and avoiding creeping implementation details to users!!

DebugInfo comes in two flavours: online and offline.

• the online implementation: computes the debug information on the fly using the compiler. This works similarly as what happens today. In other words, I only work if the compiler is available.
• the offline implementation: stores debug information previously computed in an internal data structure, and is built from an online debug info. This version works when the compiler is not available.

The API is not 100% fixed, but this already goes in a good direction.

Tests are added on the debug info API (both implementations are tested), and the system was changed making sure to keep compatibility.

Related PRs: pharo-spec/NewTools#1259

[Ducasse]

Super super super cooooooooooool

S