Separate Electron, Cypress app code, and ffmpeg into individual downloads

[flotwig]

Current Behavior

Cypress is downloaded as one large .zip (140MB zipped, 387MB unzipped on Linux) file that contains Electron, Cypress's app code, and ffmpeg.

Updates are sent out as new versions of the .zip, containing all three of those elements.

Desired Behavior

Cypress would split up the installation process into three parts:

1. Downloading Electron launcher
2. Downloading ffmpeg
3. Downloading Cypress code

Electron and ffmpeg are less-frequently-updated than Cypress itself, so we could probably help users cut down on their install sizes quite a bit after a few upgrades. Some users have noted that the installs tend to stack up after a while: #912

This would require separating Cypress from the Electron binary so that we could release them independently. Also, users would still need to be able to download an all-in-one .zip from the website for "global" mode.

[eugene-matvejev]

I do agree, we need somehow separate these things, so people might not install unneeded stuff, if they got lets say chrome installed I discussed it here: #4043

[jennifer-shehane]

I want to ask if the intent of this PR would allow each individual installation support different versions of the other installation? Or would they all have some 'min version' requirements for the other installation? Also this would not satisfy this request basically: #3228

[MeStrak]

I think the main point is separate the binaries so that they can be installed and run independently. Publishing a range of versions supported by the package would be good.

Unfortunately #6012 was closed but this would be ths solution. If the binaries were separated, Chrome and Cypress could be installed withought the need for Electron, therefore no need for Xvfb.

@jennifer-shehane I see that this has been in Stage: Ready for work since April 2019. Is work likely to start soon on this?

[MeStrak]

@flotwig do you know if dev is in progress for this?

[flotwig]

@MeStrak no, not currently. fyi, you can check the "stage" labels in issues to get an idea of what the current status of an issue is.

[jennifer-shehane]

Bringing this up from an issue with running in Heroku CI. cypress-io/cypress-example-kitchensink#324

This feature would be nice when users want to run Chrome headless only to not require some of the deps that Electron itself requires (like xvfb)