ci: start tracking CSS payload sizes for angular.io (#42584)

Previously, we only tracked the sizes of the eagerly loaded JS bundles.
However, the CSS styles (which also have a non-negligible size) must
also be downloaded and parsed by the browser, thus affecting the initial
rendering time.

This commit starts tracking the CSS styles payload sizes.
(Originally discussed in
https://github.com/angular/angular/pull/42584#discussion_r653787961)

PR Close #42584

aio/scripts/payload.sh

@@ -12,4 +12,4 @@ source ../scripts/ci/payload-size.sh
 # Provide node_modules from aio
 NODE_MODULES_BIN=$PROJECT_ROOT/aio/node_modules/.bin/
 
-trackPayloadSize "$target" "dist/*.js" true "$PROJECT_ROOT/goldens/size-tracking/aio-payloads.json"
+trackPayloadSize "$target" "dist/*.css dist/*.js" true "$PROJECT_ROOT/goldens/size-tracking/aio-payloads.json"

goldens/size-tracking/aio-payloads.json

@@ -4,7 +4,10 @@
       "uncompressed": {
         "runtime-es2017": 4619,
         "main-es2017": 456578,
-        "polyfills-es2017": 55210
+        "polyfills-es2017": 55210,
+        "styles": 69719,
+        "light-theme": 79520,
+        "dark-theme": 79419
       }
     }
   },
@@ -12,8 +15,11 @@
     "master": {
       "uncompressed": {
         "runtime-es2017": 4619,
-        "main-es2017": 456930,
-        "polyfills-es2017": 55348
+        "main-es2017": 456717,
+        "polyfills-es2017": 55348,
+        "styles": 69719,
+        "light-theme": 79520,
+        "dark-theme": 79419
       }
     }
   }