[package.json] Enable max_old_space_size Override for Desktop

[nsakaimbo]

The behavior of heap limits and garbage collection in Node 12 has changed such that attempts to build wp-desktop with updated Calypso (which is now using Node 12) fail due to memory pressure. As-is, Node will attempt to use up to the set heap allocation (max_old_space_size) of 8GB but runs into the hard 4GB limit of Circle CI's RAM at which point Node kills the build process.

// ...
lerna success - photon
lerna success - @automattic/tree-select
Rendering Complete, saving .css file...
Wrote CSS to /home/circleci/wp-desktop/calypso/public/directly.css
Rendering Complete, saving .css file...
Wrote CSS to /home/circleci/wp-desktop/calypso/public/editor.css
Killed

We need to tell Node to allocate to the heap less than the Docker container's 4GB RAM limit. However, it seems there's a fundamental flaw in the way NODE_ARGS is set such that this parameter cannot be overriden at build time.

Simplified Example

A simple example to illustrate:

"scripts": {
  "run-my-script": "ENV_VAR=default npm run my-script",
  "my-script": "echo $ENV_VAR"
}

> ENV_VAR=custom npm run run-my-script
> echo $ENV_VAR
> default

// Want "custom", but get "default"
// Not what we intend or expect

In a nutshell, the above example illustrates the problem with the way NODE_ARGS is currently set. We need to be able to override this value when building wp-desktop, but are unable to.

(Side note: For some reason, this hasn't been an issue until Node 12 updated the way memory is managed. In addition, this only seems to affect Calypso as it is built for wp-desktop. However the issue with the way NODE_ARGS is set is a problem regardless.)

Changes proposed in this Pull Request

The values of NODE_ARGS and max_old_space_size for wp-desktop should be able to be overriden per the constraints of the hardware Caypso is being built on. Using the syntax NODE_ARGS=${NODE_ARGS:---max_old_space_size=8192} ensures that the default value of 8192MB will be used unless overridden by the caller, so we can maintain the existing behavior and customize this parameter where necessary.

Testing instructions

By pointing wp-desktop at this branch, we can verify that enabling the override of the hard-coded max_old_space_size value fixes the build failure on CI for wp-desktop.

• Before: out-of-memory - process killed (build job]
• After: max_old_space_size override is respected, and Calypso build is successful (build job)

[matticbot]

Test live: https://calypso.live/?branch=do-not-hard-code-max-old-space-size

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[nsakaimbo]

Seems like some additional CI jobs were triggered by wp-desktop and lines were crossed somewhere - not sure why those jobs are showing up here. Please ignore ci/wp-desktop, ci/wp-e2e-tests-full-desktop and ci/wp-e2e-tests-full-desktop as those have no bearing on this PR.