Upgrade tfjs repo to 4.0.0

[mattsoulanille]

This major release upgrades TypeScript from 3.5.3 to 4.8.4 (#6346). It is intended to be as non-breaking as possible, but it technically has breaking changes for users of typescript<4.4. All other users should be unaffected.

When compiling projects that depend on TFJS with typescript<4.4, the following error will appear.

node_modules/@webgpu/types/dist/index.d.ts:587:16 - error TS2304: Cannot find name 'PredefinedColorSpace'.

587   colorSpace?: PredefinedColorSpace;
                   ~~~~~~~~~~~~~~~~~~~~
...

This can be fixed by upgrading TypeScript to 4.4.2 or greater, or by adding the file predefined_color_space.d.ts (name and path can be changed) with the following contents to your project to define the missing type. If this file is added, it will need to be removed when TypeScript is upgraded past 4.3.

type PredefinedColorSpace = "display-p3" | "srgb";

typescript<3.7 has the following additional error.

node_modules/@tensorflow/tfjs-core/dist/engine.d.ts:127:9 - error TS1086: An accessor cannot be declared in an ambient context.

127     get backend(): KernelBackend;
            ~~~~~~~
...

Enabling skipLibCheck suppresses this error, and upgrading to at least TypeScript 3.6.2 fixes it (although the above fix for PredefinedColorSpace will also need to be applied).

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

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This change is 

[pyu10055]

Reviewed 55 of 55 files at r1, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained

[lina128]

LGTM

Reviewable status: complete! 2 of 1 approvals obtained

[mattsoulanille]

Nightly passed