Revive packed division - add out of bounds check.

[annxingyuan]

This PR fixes tensorflow/tfjs#1324

This change works with the LSTM text generation example (which is why we turned off packed division to begin with).

Changes

• Revive packed division
• Change packed and unpacked division to return NaN if divide by zero
• Change closeness test to consider NaN and Infinity to be close so when we divide log(0) by 0 and get 0 the test passes

This change is 

[nsthorat]

Reviewed 5 of 5 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @annxingyuan, @dsmilkov, and @nsthorat)

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src/kernels/webgl/binaryop_packed_gpu.ts, line 215 at r1 (raw file):

            bool nextColOutOfBounds =
              (${channels[rank - 1]} + 1) >= ${this.outputShape[rank - 1]};
            

remove the spaces on this line

[annxingyuan]

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

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src/kernels/webgl/binaryop_packed_gpu.ts, line 215 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

remove the spaces on this line

Done