DbString is a known type in Dapper and currently there is no dedicated support in DapperAOT for it.

Current PR does 2 things regarding DbString:

1. in analyzer mode reports DAP48 and suggests to move from usage of DbString to DbValue attribute.
2. properly configures DbParameter if one of parameter members is DbString by setting .Value, .Size and .DbType

Implementation notes:

1. I have moved files in Dapper.AOT.Analyzers which are copied to the output in separate folder InGeneration
2. I have created a single code writer for such types (PreGeneratedCodeWriter), and included the generation context options in GenerateState to have a control over which pre-generated types to include in the output. I decided to do in order to avoid writing DbStringHelpers in the output even in those cases, where DbString is not even used (basically to have more clear output)

Questions:

1. I am pretty sure I messed up on how to get the size of DbString in ANSI encoding. How do we do it properly?
2. What exactly do we need to do with the DbString in UpdateParameters? Do we need to call the same setup there, or just re-assigning value is fine?

Closes #89