create SnapshotWithBlobs interface

[dannimad]

-Unify snapshotree and its blobs types into a single interface SnapshotWithBlobs given that they refer to the same summary data and represent just different parts of the same summary.
-Move PendingContainerState interfaces to serializedStateManager
-Fix tests types

There are a couple of changes pending:

1. Get rid of ISnapshotTreeWithBlobContents which unfortunately it's harder to do than it seems.
2. Initialize this.snapshot with pendinglocalstate value from the constructor. There is no need to wait until fetchSnapshot.

[msfluid-bot]

Baseline CI build failed, cannot generate bundle analysis at this time

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Baseline commit: 7d00e81

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