fix(misc): update package.json only if needed

[juristr]

Adjusts the schematic to only touch the package.json if really required.

ISSUES CLOSED: #2317

@FrozenPandaz could you give this a look.

Two open questions related to this:

• the verification of whether the package.json should be touched could be moved directly to the ast-utils.ts class and integrated in the addDepsToPackageJson. Let me know what you think about that.
• how do we test this? Just verifying the schematic result tree for the package.json in the unit test doesn't really work. Alternatively we could add an e2e and verify the log output. that would work for sure

[FrozenPandaz]

the verification of whether the package.json should be touched could be moved directly to the ast-utils.ts class and integrated in the addDepsToPackageJson

Can we move it there please?

how do we test this?

The host should have a list of actions that will be performed:

https://github.com/nrwl/nx/blob/master/packages/workspace/src/utils/rules/format-files.ts#L26

We can make sure that UPDATE package.json is not in that list after running this Rule

[vsavkin]

@juristr needs rebasing, other than that looks good.

[juristr]

@vsavkin I'm probably gonna make a small modification here tomorrow that might avoid the need to change the API of the addDepsToPackageJson to avoid having to pass the Tree & thus change all those other files.

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