refactor(ivy): do not generate providedIn: null (#34116)

We should only generate the `providedIn` property in injectable
defs if it has a non-null value. `null` does not communicate
any information to the runtime that isn't communicated already
by the absence of the property.

This should give us some modest code size savings.

PR Close #34116

integration/_payload-limits.json

@@ -30,7 +30,7 @@
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+        "main-es2015": 136594,
         "polyfills-es2015": 37494
       }
     }
@@ -39,7 +39,7 @@
     "master": {
       "uncompressed": {
         "runtime-es2015": 2289,
-        "main-es2015": 267389,
+        "main-es2015": 266648,
         "polyfills-es2015": 36808,
         "5-es2015": 751
       }
@@ -49,7 +49,7 @@
     "master": {
       "uncompressed": {
         "runtime-es2015": 2289,
-        "main-es2015": 226528,
+        "main-es2015": 225787,
         "polyfills-es2015": 36808,
         "5-es2015": 779
       }