Offer `split()` expression function as a pair for `join()`

Describe the enhancement Provide an expression function split() as a pair to join()

Code Snippet

name: build
on: push
jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        os: ${{split(github.event.inputs.os, ' ')}}
    steps:
      - run: build

Additional information This is based on PowerDNS/pdns#11960 and would greatly simplify: https://github.com/PowerDNS/pdns/blob/d41e087ca092ff60f9fc79e177f8a61bfdffd1f9/.github/workflows/builder-dispatch.yml#L38-L55

NOTE: if the feature request has been agreed upon then the assignee will create an ADR. See docs/adrs/README.md

[Habbie]

You would have to add those, yes. So input something like "linux","windows 95","windows me" when triggering the workflow_dispatch run.

Understood - at that point the user might as well type actual JSON I think.

[jsoref]

act is an alternate implementation of runner. I definitely want it here (and then it’d have to be implemented there).