Add kernel RaggedRange for CPU and WebGL backend

[ahmedsabie]

To see the logs from the Cloud Build CI, please join either our discussion or announcement mailing list.

---

This change is 

[mattsoulanille]

Just a quick review removing "all rights reserved" from the license headers of new files (don't change existing files).

[lina128]

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

---

tfjs-backend-cpu/src/kernels/RaggedRange_impl.ts line 20 at r1 (raw file):

import {DataType, TypedArray, util} from '@tensorflow/tfjs-core';

const INT32_MAX = 2147483647;

Why not use Number.MAX_SAFE_INTEGER?

Code quote:

const INT32_MAX = 2147483647

[pyu10055]

thank you for adding this op.

Reviewed 12 of 12 files at r1, all commit messages.
Reviewable status: complete! 2 of 1 approvals obtained (waiting on @ahmedsabie)

[mattsoulanille]

LGTM