Coverlet: Add support for TeamCity using service messages

[obtuse-whoosh]

I've noticed that TeamCity does not support any of the output formats currently offered by this tool and the ReportGenerator tool. It would be a simple thing to add some support for writing TeamCity service messages out to the console, since we already print some statistics.

Some Statistics that are easily supported:

| TeamCity Statistic Key | Description |
| :--- | :----: |
| CodeCoverageL | Line Coverage |
| CodeCoverageC | Class Coverage |
| CodeCoverageM | Method Coverage |
| CodeCoverageAbsLTotal | The total number of lines |
| CodeCoverageAbsLCovered | The number of covered lines |
| CodeCoverageAbsCTotal | The total number of classes |
| CodeCoverageAbsCCovered | The number of covered classes |
| CodeCoverageAbsMTotal | The total number of methods |
| CodeCoverageAbsMCovered | The number of covered methods |

Some statistics that would require extra work to support:

| TeamCity Statistic Key | Description |
| :--- | :----: |
| CodeCoverageS | Statement Coverage |
| CodeCoverageB | Block Coverage |
| CodeCoverageR | Branch Coverage |
| CodeCoverageAbsSTotal | The total number of statements |
| CodeCoverageAbsSCovered | The number of covered statements |
| CodeCoverageAbsBTotal | The total number of blocks |
| CodeCoverageAbsBCovered | The number of covered blocks |
| CodeCoverageAbsRTotal | The total number of branches |
| CodeCoverageAbsRCovered | The number of covered branches |

See the documentation here for more info about TeamCity service messages
See the documentation here for more info about TeamCity statistics

[obtuse-whoosh]

Essentially all that would need to be added would be a few lines like:

Console.WriteLine("##teamcity[buildStatisticValue key='CodeCoverageC' value='39.6']");
Console.WriteLine("##teamcity[buildStatisticValue key='CodeCoverageAbsCCovered' value='53']");
Console.WriteLine("##teamcity[buildStatisticValue key='CodeCoverageAbsCTotal' value='134']");

and a command line switch to toggle this output. A good example of this can be found in a blog post here

[obtuse-whoosh]

BTW Reptarsrage is my other account, and the PR for this is #227

[obtuse-whoosh]

@tonerdo What's the eta for the next release?

[tonerdo]

See latest release: https://www.nuget.org/packages/coverlet.msbuild/2.3.2

[gilescope]

Good start. Would be great to get an in-depth view that was on parity with the other formats.
Seems TC has service message support for sucking in a file:

teamcity[importData type='dotNetCoverage' tool='' path='']

where tool name can be partcover, ncover or ncover3. (or Teamcity's coverage.xml format)

[Reptarsrage]

@gilescope You should open a new issue that can be tracked/prioritized by the code owners, if you haven't done that already.