Upcoming metadata changes in V8 6.9

[cjihrig]

The V8 6.9 update requires the following adjustments to the
postmortem debugging metadata constants:

• v8dbg_class_SharedFunctionInfo__function_identifier__Object
  Use: v8dbg_class_SharedFunctionInfo__function_identifier_or_debug_info__Object

• v8dbg_class_SharedFunctionInfo__end_position__int
  Use: v8dbg_class_UncompiledData__end_position__int32_t

• v8dbg_class_SharedFunctionInfo__start_position_and_type__int
  Use: v8dbg_class_UncompiledData__start_position__int32_t

• v8dbg_sharedfunctioninfo_start_position_mask and v8dbg_sharedfunctioninfo_start_position_shift
  Removed. Use: v8dbg_class_UncompiledData__start_position__int32_t

• v8dbg_scopeinfo_idx_nstacklocals has been removed

See: nodejs/node@541e8c2
Refs: v8/v8@39e2d97
Refs: v8/v8@467eb14
Refs: v8/v8@c51bcd1

[mmarchini]

Related: #202

[mmarchini]

Fixed by #247