Run predictive jest jobs earlier by separating out fixture-using specs

What does this MR do and why?

Similar to !153447 (merged), this MR lets predictive jest tests run up to 16 minutes earlier in pipelines of unapproved MRs, leading to much faster feedback for developers when initially developing their change (fail fast!).

This also causes most of these pipelines to finish up to 5 minutes earlier. All jest specs that require fixtures will run later in jest-with-fixtures predictive.

This change is tested in !154939 (closed).

The next iteration could be to dynamically skip the fixture generation in unapproved MR pipelines if we don’t need fixtures, so we could have even faster frontend pipelines during development.

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