Gather performance stats with rollup-plugin-visualiser

[domoscargin]

What

Use rollup-plugin-visualiser to gather stats on code performance.

This will build off work done in:

• [DO NOT MERGE] Use rollup-plugin-visualizer to gather some stats on the file #3109
• [DO NOT MERGE] Provide a standalone way to run rollup for stats gathering #3115

We want to initially just get rollup-plugin-visualiser working with our code and outputting info from our build. This will likely require creating a standalone stats-gathering rollup build, since the plugin requires rollup 3, and we're pinned to 0.59.4 for IE8 compatibility.

Why

As we're making changes to the way our JavaScript works, and other architectural changes, we'd like to keep track of how our changes impact the files we distribute.

Who needs to work on this

Developer

Who needs to review this

Developer

Done when

• We can output stats and visual data from rollup-plugin-visualiser: [SPIKE] Collecting performance information #3239
• We've decided which files and modules we want to track
• Made issues for next steps:
  • Compare diff between pull requests and base branches
  • Github action to comment on PRs with these stats
  • Set up a way to store the data gathered to use for analysing trends
  • Decide what "good" looks like (after monitoring stats for a while)

[domoscargin]

Closing in favour of #3279