Now that exceptions are not _parsed_ anymore (#513 and #637), keeping the `ExceptionInfo` and `StackFrameInfo` internal classes doesn't make much sense anymore. The `Exception` and `StackFrame` types can be used by the `ExceptionFormatter` class directly, without conversion.
This is the natural extension of #513 which already removed a lot of regex parsing.
The `ExceptionParser` class is renamed into `ExceptionConverter` because there is no more string parsing performed at all. `Exception` is converted into `ExceptionInfo` and `StackFrame` is converted into `StackFrameInfo`.
The generic parameters were double escaped and would display as `[[T0,T1,TRet]]` instead of `[T0,T1,TRet]`. This is because the `builder.AppendWithStyle` method already escapes its value so the caller must not escape the passed value.
On .NET Framework, `exception.ToString()` uses a slightly different format than on .NET Core.
So in order to properly transform an `Exception` into an `ExceptionInfo` on both .NET Core and .NET Framework we use `exception.StackTrace` + `exception.InnerException`. As an added benefit, it greatly simplifies the implementation of the `ExceptionParser` class.
