chore: implement integration testing

[DeagleGross]

So far the only testing available is "eye-testing":

1. write user code input
2. generate intercepted code out of it
3. check if generated code makes sense.

It would be great to have some integration tests using generated bits against some database to ensure code works. I created Dapper.AOT.Test.Integration project as a launcher of tests and Dapper.AOT.Test.Integration.Executables project as user code (similar to input we had before).

Tests work in this way:

• Use a type from Executables (I will further call it "user code") and parse the code as text
• Create compilation out of it which includes minimum amount of assembly references to make it work
• Run DapperInterceptorGenerator on that compilation and get new compilation instance with both user code and generated bits
• Run compilation.Emit() to get a built-in assembly in the code
• Via reflection access the user code type specified on the first step and activate an instance of the class
• Execute the code passing pre-created IDbConnection.

To make sure that generated interception code is actually being invoked, I also adjusted DapperInterceptorGenerator to include such a code line:

global::Dapper.AOT.Test.Integration.Executables.Recording.InterceptorRecorderResolver.Resolve().Record();

Since Dapper.AOT.Test.Integration.Executables assembly is anyway referenced to the compilation built during a test execution, we have access to all types there. InterceptorRecorderResolver is a container for IInterceptorRecorder -> test code can register any implementation of recorder to collect all necessary information it can. The implementation I have provided does the following:

• get the StackTrace and takes only last 15 frames out of it
• finds invocation of intercepted code (generated bits)
• finds invocation of user code
• ensures that user code is invoked before intercepted code (which is logical)

In such a manner we can be sure that generated code is actually executed.

Closes #122