Simplify tracked state at each summarizerNode (microsoft#22095)

This PR removes some redundant tracked states that are maintained by
each summarizerNode. Following are the list of changes:
- Disable incremental summaries and perform complete summarization
instead (the first time), for the cases where base snapshot was created
in an older document where isolated channels were disabled (i.e.
`.channels` concept was not there in a node path).
[`containerRuntime.ts`]

- `SummaryNode` is removed. SummaryNode was tracking base, additional
etc. path related information for each node, which was convoluting the
code too much. It has been simplified by always providing the path
information to the summarizerNode as a `_summaryHandleId`. Every time a
child node it created, it's path is stored as _summaryHandleId and thus
removes the need for `SummaryNode`.
[`summarizerNode.ts`, `summarizerNodeUtils.ts`].

- `latestSummary:SummaryNode` is replaced with just
`_lastSummaryreferenceSequenceNumber`.

- `PendingSummaryInfo` has been introduced to solve for the other half
of the logic that was fulfilled previously by `SummaryNode` i.e.
maintaining the state of pending summaries submitted so far. Instead of
saving path and referenceSequenceNumber both, we now just maintain
`referenceSequenceNumber`. Saves memory footprint, and simplifies code.
[`summarizerNode.ts`, `summarizerNodeUtils.ts`]

- The above changes also reflected in`summarizerNodeWithGC.ts`.

packages/runtime/container-runtime/src/containerRuntime.ts

@@ -1711,15 +1711,21 @@ export class ContainerRuntime
 		});
 
 		const loadedFromSequenceNumber = this.deltaManager.initialSequenceNumber;
+		// If the base snapshot was generated when isolated channels were disabled, set the summary reference
+		// sequence to undefined so that this snapshot will not be used for incremental summaries. This is for
+		// back-compat and will rarely happen so its okay to re-summarize everything in the first summary.
+		const summaryReferenceSequenceNumber =
+			baseSnapshot === undefined || metadata?.disableIsolatedChannels === true
+				? undefined
+				: loadedFromSequenceNumber;
 		this.summarizerNode = createRootSummarizerNodeWithGC(
 			createChildLogger({ logger: this.logger, namespace: "SummarizerNode" }),
 			// Summarize function to call when summarize is called. Summarizer node always tracks summary state.
 			async (fullTree: boolean, trackState: boolean, telemetryContext?: ITelemetryContext) =>
 				this.summarizeInternal(fullTree, trackState, telemetryContext),
 			// Latest change sequence number, no changes since summary applied yet
 			loadedFromSequenceNumber,
-			// Summary reference sequence number, undefined if no summary yet
-			baseSnapshot !== undefined ? loadedFromSequenceNumber : undefined,
+			summaryReferenceSequenceNumber,
 			{
 				// Must set to false to prevent sending summary handle which would be pointing to
 				// a summary with an older protocol state.
@@ -1733,10 +1739,6 @@ export class ContainerRuntime
 			async () => this.garbageCollector.getBaseGCDetails(),
 		);
 
-		if (baseSnapshot) {
-			this.summarizerNode.updateBaseSummaryState(baseSnapshot);
-		}
-
 		const parentContext = wrapContext(this);
 
 		if (snapshotWithContents !== undefined) {

packages/runtime/container-runtime/src/dataStoreContext.ts

@@ -1034,9 +1034,6 @@ export class RemoteFluidDataStoreContext extends FluidDataStoreContext {
 			this._baseSnapshot = props.snapshot;
 			this.isSnapshotInISnapshotFormat = false;
 		}
-		if (this._baseSnapshot !== undefined) {
-			this.summarizerNode.updateBaseSummaryState(this._baseSnapshot);
-		}
 	}
 
 	/*