Make flushMode immutable for a container. Deprecate ContainerRuntime.setFlushMode()

[agarwal-navin]

From the conversation in #9432, we should make flushMode immutable.

Primary reason for this work is to enable / make it easier to do

• Remove flushMode tracking and validation in PendingStateManager #9481

[andre4i]

To add:

• flushmode may be set via IContainerRuntimeOptions
• must remove the IContainerRuntimeBase.setFlushMode() function
• must follow the guidelines at https://github.com/microsoft/FluidFramework/wiki/API-Deprecation
• must ensure whether or not someone is using actually using this API (add a telemetry event when this property is toggled) - my guess is that the feature is not currently used
• must simplify all other code paths which assume flushmode changes during the lifetime of the runtime (separate workitem for this, as the work is slightly more involved and orthogonal to the API deprecation).

[andre4i]

Deprecated API

IContainerRuntimeBase.setFlushMode(mode: FlushMode): void;

Context

The API is not currently used and enables a set of scenarios which should not be supported. Maintaining this API is costly and it adds a non-trivial amount of complexity to the adjacent logic.

Approach

FlushMode can be set at runtime creation, using IContainerRuntimeOptions and will remain immutable for the lifetime of the object.

Workarounds for the existing scenarios:

• Runtime has FlushMode.TurnBased and the client needs ad-hoc behavior similar to FlushMode.Immediate? Force a JS turn after each operation (use a construct such as Promise.resolve().then)
• Runtime has FlushMode.Immediate and the client needs ad-hoc behavior similar to FlushMode.TurnBased? Use IContainerRuntimeBase.orderSequentially

Dependencies
n/a

Compatibility Concerns
n/a

Phases

• Mark the API as deprecated and emit a telemetry event for its use
• Remove the API and all it's usages

Expected Timeline

• 0.60

Open Questions

TBD

[andre4i]

Confirmed the API is not currently used in Bohemia and Whiteboard.

[kian-thompson]

Closed to track in AB#393