Generalize the tensor container to arbitrary depth

[dsmilkov]

FEATURE

Currently, calling tf.dispose(obj) or tf.tidy(() => obj) results in walking the obj for depth of 1 and disposing of any tensors found.

With this change obj is walked to arbitrary depth with cycle-detection to defend against cyclical objects.

This makes tf.tidy() and tf.dispose() more useful in practice.

Also rename util.extractTensorsFromContainer to util.getTensorsFromContainer since we are not modifying (extracting from) the container.

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For more info see: https://github.com/tensorflow/tfjs/blob/master/DEVELOPMENT.md

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This change is 

[nsthorat]

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Review status: 0 of 5 files reviewed at latest revision, all discussions resolved.

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src/util.ts, line 459 at r1 (raw file):

export function getTensorsInContainer(result: TensorContainer): Tensor[] {
  const list: Tensor[] = [];
  const seen = new Set<{}|void>();

do you need |void?

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Comments from Reviewable

[dsmilkov]

Review status: 0 of 5 files reviewed at latest revision, 1 unresolved discussion, some commit checks pending.

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src/util.ts, line 459 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

do you need |void?

yeah because TensorContainer is void|otherStuff and void is needed for tidy's that won't return anything.

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Comments from Reviewable