Easier code coverage collection for C# contract tests

[majordutch]

A helpful feature for C# contract tests would be an easier way to collect code coverage for the original contract source from the neo-test execution.

@devhawk provided some insightful information regarding this:

TestApplicationEngine automatically collects coverage information while 
executing. You can retrieve it via the GetHitMap and GetBranchMap methods

The Get*Map methods take a contract hash parameter - coverage information 
is tracked separately per contract

The hit map is a dictionary mapping NeoVM addresses to a hit count (i.e. 
how many times that specific instruction was executed)

the branch map is a dictionary mapping NeoVM addresses of branch instructions 
to a pair of hit counts - how many times this instruction branched vs continued

So that's the good news. Bad news is that there is no built-in mechanism to 
aggregate the info or publish it in a format that existing code coverage tools 
can use

There's also a need to map NeoVM address to source code lines. I assume folks 
are more interested in a source level view of coverage rather than an assembly 
level view

There is code in the test runner project (part of the neo test repo, a tool to 
enable non-c# developers to run tests) that iterates sequence points from debug 
info to retrieve hit/branch coverage info, but it's not in an easy-to-reuse 
method, it's just part of WriteResultsAsync method.

[devhawk]

This requires a Data Collector (https://github.com/Microsoft/vstest-docs/blob/main/docs/analyze.md).