Update to use new actions-utils that is aware of ALL_CHANGED_FILES (#28)

## Summary:
See Khan/actions-utils#14

## Test plan:
I updated the workflow to set up the ALL_CHANGED_FILES variable. Our other workflows that use eslint-action will want to add those setup steps as well.

Author: jaredly

Reviewers: jeresig, jaredly

Required Reviewers: 

Approved by: jeresig

Checks: ❌ lint_and_unit, ✅ autofix

Pull request URL: #28

.github/workflow-templates/_setup.yml

@@ -1,9 +1,26 @@
 
 setup:
   checkout:
-  - uses: actions/checkout@v1
-    name: get the repo
+  - uses: actions/checkout@v2
   yarn:
     setup: checkout
     steps:
       - run: yarn
+
+  # This gets the list of files that changed in the current pull-request
+  # and puts then onto the ALL_CHANGED_FILES env variable, which several
+  # of our actions will use.
+  changed-files:
+    steps:
+      - name: Get All Changed Files
+        uses: jaredly/[email protected]
+        id: changed
+        with:
+          format: 'json' # robust to filenames with spaces
+          absolute: true # our tooling expects absolute paths
+
+      # Now we put it on the environment so that it can be picked up by
+      # anything that uses actions-utils (e.g. eslint-action, jest-action, etc.)
+      - uses: allenevans/[email protected]
+        with:
+          ALL_CHANGED_FILES: '${{ steps.changed.outputs.added_modified }}'

.github/workflow-templates/pr-actions.yml

@@ -11,23 +11,23 @@ jobs:
     steps:
       - name: Run eslint
         uses: Khan/eslint-action@main
-        setup: yarn
+        setup: [yarn, changed-files]
         with:
           eslint-lib: ./node_modules/eslint
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Run jest tests
         uses: Khan/jest-action@main
-        setup: yarn
+        setup: [yarn, changed-files]
         with:
           jest-bin: ./node_modules/.bin/jest
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Run jest coverage
         uses: Khan/jest-coverage-action@main
-        setup: yarn
+        setup: [yarn, changed-files]
         with:
           jest-bin: ./node_modules/.bin/jest
           coverage-data-path: ./coverage/coverage-final.json
@@ -36,15 +36,15 @@ jobs:
 
       - name: Run flow
         uses: Khan/flow-action@main
-        setup: yarn
+        setup: [yarn, changed-files]
         with:
           flow-bin: ./node_modules/.bin/flow
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Run flow coverage
         uses: Khan/flow-coverage-action@main
-        setup: yarn
+        setup: [yarn, changed-files]
         with:
           flow-bin: ./node_modules/.bin/flow
         env: