Add coverage to GH actions and rework part of them (#1987)

.github/actions/save-coverage-data/action.yml

@@ -0,0 +1,17 @@
+name: 'Merge and upload coverage data'
+description: 'Compresses and uploads the coverage data as an artifact'
+
+runs:
+  using: "composite"
+  steps:
+    - name: Merge coverage data
+      shell: bash -ex {0}
+      run: scripts/coverage "--profraw-prefix=$GITHUB_JOB" --dir=/tmp/neon/coverage/ merge
+
+    - name: Upload coverage data
+      uses: actions/upload-artifact@v3
+      with:
+        retention-days: 7
+        if-no-files-found: error
+        name: coverage-data-artifact
+        path: /tmp/neon/coverage/