Extracting common dwarf reader functionality into its own area

[epipho]

Searching by name through the dwarf data is not sufficient for many advanced use cases. This is the beginning of an attempt to rectify this by creating a more intelligent reader.

Current functionality:

• Seek reader to function by pc. Replaces looking up the function name by pc and then looking up the function by name.
• Seek reader to a specific dwarf entry.
• Traverse scope variables.

Assuming you approve of this direction, the next PR would add:

• Variable -> Base type mapping
• Member data traversal
• Read stack program instructions from an entry

[derekparker]

Should the entry be returned here? It's just returning the entry that was passed in, maybe just return the error?

[epipho]

Probably not, I had this idea that all the seek functions should have the same signature but in retrospect I think that is unnecessary.

[derekparker]

A few notes but I really like this.

[epipho]

Moved ThreadContext.Reader to DebuggedProcess.DwarfReader and squashed down the commits.

Glad you like it, with some more work it will simplify a lot of the code while increasing the accuracy.

[derekparker]

Merged.