refactor(core): rename ngInjectorDef to ɵinj (#33151)

Injector defs are not considered public API, so the property
that contains them should be prefixed with Angular's marker
for "private" ('ɵ') to discourage apps from relying on def
APIs directly.

This commit adds the prefix and shortens the name from
ngInjectorDef to inj. This is because property names
cannot be minified by Uglify without turning on property
mangling (which most apps have turned off) and are thus
size-sensitive.

PR Close #33151

packages/compiler/design/separate_compilation.md

@@ -73,7 +73,7 @@ class:
 | `hostListeners`     | `ɵdir`                |
 | `hostProperties`    | `ɵdir`                |
 | `hostAttributes`    | `ɵdir`                |
-| `providers`         | `ngInjectorDef`       |
+| `providers`         | `ɵinj`                |
 | `viewProviders`     | `ɵcmp`                |
 | `queries`           | `ɵdir`                |
 | `guards`            | not used              |
@@ -282,7 +282,7 @@ export class MyPipe {
 The metadata for a module is transformed by:
 
 1. Remove the `@NgModule` directive.
-2. Add  `"ngInjectorDef": {}` static field.
+2. Add  `"ɵinj": {}` static field.
 3. Add `"ngModuleScope": <module-scope>` static field.
 
 The scope value is an array the following type:
@@ -329,7 +329,7 @@ export class MyModule {}
 *my.module.js*
 ```js
 export class MyModule {
-  static ngInjectorDef = ɵɵdefineInjector(...);
+  static ɵinj = ɵɵdefineInjector(...);
 }
 ```
 
@@ -342,7 +342,7 @@ export class MyModule {
     "MyModule": {
       "__symbolic": "class",
       "statics": {
-        "ngInjectorDef": {},
+        "ɵinj": {},
         "ngModuleScope": [
           {
             "type": {
@@ -389,7 +389,7 @@ manually written as:
 
 ```ts
 export class MyModule {
-  static ngInjectorDef = ɵɵdefineInjector({
+  static ɵinj = ɵɵdefineInjector({
     providers: [{
       provide: Service, useClass: ServiceImpl
     }],
@@ -440,7 +440,7 @@ properties by including a `// @__BUILD_OPTIMIZER_REMOVE_` comment:
 
 ```ts
 export class MyModule {
-  static ngInjectorDef = ɵɵdefineInjector({
+  static ɵinj = ɵɵdefineInjector({
     providers: [{
       provide: Service, useClass: ServiceImpl
     }],