Break build when change impacts on file sizes/modules content is too big

[romaricpascal]

Part of #3279

What

Automatically break the build when the changes introduced in a branch yield too big an impact on file sizes/modules content.

Why

It'll make it easier to spot big impacts, and make consistent from one PR to another what's considered as such.

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• We've gathered data from multiple PRs about what's a "normal" impact on file size/modules content
• We've decided on criteria for what constitutes too big a change ¹
• A Github workflow breaks the build when changes meet those criteria ²

Footnotes

1. We'll likely want to consider comparing relative changes, rather than absolute ones ↩

2. We'll need to design a way to get the PR to go through anyway, as the large variation may be justified (eg. new component, big tidy-up...) ↩