Frontend: Move toEmit jest matchers to shared workspace (#108610)

* feat(test-utils): move the toEmitValue/s jest matchers to test-utils and add test script

* chore(jest): update configs to use matchers from test-utils package

* ci(frontend-tests): hook up packages tests

* fix(test-utils): re-export matchers from index.ts so packages that include setupTests don't error

* ci(pr-frontend-unit-tests): add frontend-packages-unit-tests to list of required unit tests

* Update packages/grafana-test-utils/README.md

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

---------

Co-authored-by: Ivana Huckova <30407135+ivanahuckova@users.noreply.github.com>

.github/workflows/pr-frontend-unit-tests.yml

@@ -107,6 +107,24 @@ jobs:
     - run: yarn install --immutable --check-cache
     - run: yarn run plugin:test:ci
 
+  frontend-packages-unit-tests:
+    needs: detect-changes
+    if: needs.detect-changes.outputs.changed == 'true'
+    runs-on: ubuntu-latest-8-cores
+    name: "Packages unit tests"
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        persist-credentials: false
+    - uses: actions/setup-node@v4
+      with:
+        node-version-file: '.nvmrc'
+        cache: 'yarn'
+        cache-dependency-path: 'yarn.lock'
+    - run: yarn install --immutable --check-cache
+    - run: yarn run packages:test:ci
+
+
   # This is the job that is actually required by rulesets.
   # We need to require EITHER the OSS or the Enterprise job to pass.
   # However, if one is skipped, GitHub won't flat-map the shards,
@@ -116,6 +134,7 @@ jobs:
       - frontend-unit-tests
       - frontend-unit-tests-enterprise
       - frontend-decoupled-plugin-tests
+      - frontend-packages-unit-tests
     # always() is the best function here.
     # success() || failure() will skip this function if any need is also skipped.
     # That means conditional test suites will fail the entire requirement check.