Add method dispatching TaskEntity base class

[jviau]

resolves #164

Adds a TaskEntity abstract class which can be used for implementing entities where all public methods are considered operations.

What is supported?

Customers can derive from TaskEntity and add public methods to their type which will be considered operations. These public methods work as follows:

1. The return value is the response to the operation caller (if available)
2. input, entity context, and entity operation are supported as parameters.
3. Default values for the input parameter is supported.
4. The input parameter does not need to be called input. It is defined as any parameter which does not match TaskEntityContext or TaskEntityOperation.
5. Bound parameters cannot be duplicate, meaning a max of 3 parameters and only 1 of each can match input, context, and operation.
6. Methods cannot return Task or ValueTask (until we determine this support is needed).
   1. Added this restriction as I am unsure how an async entity would even behave, given the current implementation in DF is based on orchestrations.

[sebastianburckhardt]

Methods cannot return Task or ValueTask (until we determine this support is needed)

I think we need to support this. It is very common for entity operations to perform I/O and restricting our users to do synchronous I/O is pretty terrible (in fact, synchronous I/O is "forbidden" in some contexts).

[sebastianburckhardt]

A few minor suggestions, looks good overall.

[jviau]

I think we need to support this. It is very common for entity operations to perform I/O and restricting our users to do synchronous I/O is pretty terrible (in fact, synchronous I/O is "forbidden" in some contexts).

Ah okay, so we do allow for yielding of the thread in an entity. Good to know. Will add that support.