Refactor release script.

[lina128]

The release process will change to

1. which release unit (union, vis, react-native, or website),
2. which phase. The release branch should be auto generated, following a pattern ${release_unit}_${release_version}.

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This change is 

[dsmilkov]

Great! Wait for Nikhil as well.

Reviewed 1 of 1 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @dsmilkov, @lina128, @nsthorat, and @pyu10055)

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scripts/release.ts, line 222 at r1 (raw file):

    if (phaseInt !== 0) {
      // Phase0 should be published and release branch should have been created.
      const latestVersion = $(`npm view @tensorflow/${phases[0].packages[0]} dist-tags.latest`);

nit: use string concat (+) to break this string in 2 and keep 80 width, or move the cmd to a separate variable.

[nsthorat]

Reviewable status: complete! 2 of 1 approvals obtained (waiting on @lina128, @nsthorat, and @pyu10055)

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scripts/release.ts, line 107 at r1 (raw file):

};

const TFJS = {

how about

const TFJS_RELEASE_UNIT: ReleaseUnit = {

here and below

[lina128]

Thank you for the comments, change done. Thank you @dsmilkov and @nsthorat!