Add TensorListLength op

[Linchenn]

Add TensorListLength op, as mentioned in Issue.

Here is the corresponding TensorListLength op in TensorFlow:
https://www.tensorflow.org/api_docs/python/tf/raw_ops/TensorListLength?hl=vi

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This change is 

[pyu10055]

Great work, thank you Lin!
Please always provide meaningful CL description that helps the reviewers (ie links to TF op definition and TF op document).

Reviewable status: 0 of 1 approvals obtained (waiting on @Linchenn)

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tfjs-converter/src/operations/executors/control_executor_test.ts, line 1010 at r1 (raw file):

        expect(size.length).toEqual(1);
        expect(size[0].shape).toEqual([]);
        test_util.expectArraysClose(size[0].dataSync(), new Int32Array([2]));

you can use a simple array [2] directly.

[Linchenn]

Updated the description. Thank you Ping!

Reviewable status: 0 of 1 approvals obtained (waiting on @pyu10055)

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tfjs-converter/src/operations/executors/control_executor_test.ts, line 1010 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

you can use a simple array [2] directly.

Done.

[pyu10055]

Reviewed 4 of 5 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @Linchenn)

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tfjs-converter/src/operations/executors/control_executor_test.ts, line 1010 at r1 (raw file):

Previously, Linchenn wrote…

Done.

will the following work?

test_util.expectArraysClose(size[0].dataSync(), [2]);

Code quote:

test_util.expectArraysClose(size[0].dataSync(), new Array([2]));

[Linchenn]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @pyu10055)

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tfjs-converter/src/operations/executors/control_executor_test.ts, line 1010 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

will the following work?

test_util.expectArraysClose(size[0].dataSync(), [2]);

Done. Thank you!