ci: add lint error for files with missing trailing new-line (#42478)

For quite a while it is an unspoken convention to add a trailing
new-line files within the Angular repository. This was never enforced
automatically, but has been frequently raised in pull requests through
manual review. This commit sets up a lint rule so that this is
"officially" enforced and doesn't require manual review.

PR Close #42478

tslint.json

@@ -6,6 +6,7 @@
     "node_modules/tslint-no-toplevel-property-access/rules"
   ],
   "rules": {
+    "eofline": true,
     "file-header": [
       true,
       {
@@ -56,6 +57,7 @@
     ]
   },
   "jsRules": {
+    "eofline": true,
     "file-header": [
       true,
       {