Moving RuntimeContext check inside ReminderRegistry

[cmeyertons]

Motivation

In unit testing libraries (such as OrleansTestKit) the RuntimeContext check for reminder-based grain calls proves very challenging.

Because RuntimeContext uses a thread-local mechanism, it becomes non-trivial to ensure the unit test runs on the same thread as the calling code (imagine some IO-bound async behavior happening between the unit test & the Reminder call)

This is related to some of the conversation going on in OrleansContrib/OrleansTestKit#134

Also related to #8387 - RuntimeContext hard to test

Proposed Fix

Move the RuntimeContext check into the ReminderRegistry so that it sits behind a stubbable testing seam interface instead of residing in an extension method. This fix should have very similar performance as the prior code.

This change also provides more consistent w/ the Timer Registry implementation, which defers this check to inside the GrainTimer code

Alternatives considered:

1. Extending ReminderOptions to control if the RuntimeContext check occurs
2. Implementing a singleton IReminderRegistryResolver that provides a testing seam to control this logic.

cc @ReubenBond @seniorquico

Microsoft Reviewers: Open in CodeFlow

[ReubenBond]

Beautiful, thank you!