PD-6016 fix karma spec discovery, restoring 686 tests from 1

src/test.ts was configured as the karma main but contained only the
zone.js import and initTestEnvironment, without the require.context that
pulls in spec files. With a main set, the builder loads only that entry,
so ng test ran 1 test while 334 spec files sat unexecuted. The suite has
effectively been a no-op, which is how a regression can land in a file
that ships with tests.

Declare zone.js/testing alongside the existing polyfills and drop main,
which lets the builder discover specs from tsconfig.spec.json. Delete
test.ts, now unreachable, and drop it from the spec tsconfig files list.

Author: cryptalith

angular.json

@@ -419,8 +419,7 @@
         "test": {
           "builder": "@angular-devkit/build-angular:karma",
           "options": {
-            "main": "src/test.ts",
-            "polyfills": "src/polyfills.ts",
+            "polyfills": ["src/polyfills.ts", "zone.js/testing"],
             "tsConfig": "src/tsconfig.spec.json",
             "karmaConfig": "src/karma.conf.js",
             "styles": [

src/test.ts

@@ -4,6 +4,6 @@
     "outDir": "../out-tsc/spec",
     "types": ["jasmine", "node"]
   },
-  "files": ["test.ts", "polyfills.ts"],
+  "files": ["polyfills.ts"],
   "include": ["**/*.spec.ts", "**/*.d.ts"]
 }