Upload vitest browser screenshots as CI artifacts

[hl662]

Building off of #7203, core-frontend's vitest.config.mts has screenshotFailures disabled, until we can figure out a way to integrate it into our CI if possible. We also want to update our gitignore to ignore output files coming from whichever folder we decide to put these screenshots in.

Also need to make sure every time we run a browser based vitest, the screenshot folder could get cleaned up prior.