docs($compile): update preAssignBindingsEnabled description

Previously, the changelog and migration guide did not mention the fact
that this only applies to controllers which are part of a
directive/component.

This commit ensures the changelog and migration guide mentions this explicitly.

Closes #15740

Closes #16162

Author: frederikprijck

CHANGELOG.md

@@ -700,10 +700,10 @@ consolidating all the changes shown in the previous 1.6.0 release candidates.**
 - **feat($compile): set preAssignBindingsEnabled to false by default
   ([bcd0d4](https://github.com/angular/angular.js/commit/bcd0d4d896d0dfdd988ff4f849c1d40366125858))**:
 
-Previously, `$compileProvider.preAssignBindingsEnabled` was
-set to true by default. This means bindings were pre-assigned in component
-constructors. In Angular 1.5+ the place to put the initialization logic
-relying on bindings being present is the controller `$onInit` method.
+Previously, `$compileProvider.preAssignBindingsEnabled` was set to true by default. This means
+bindings were pre-assigned on component/directive controller instances (which made them available
+inside the constructors). In Angular 1.5+ the place to put the initialization logic relying on
+bindings being present is the controller's `$onInit` method.
 
 To migrate follow the example below:
 

docs/content/guide/migration.ngdoc

@@ -75,8 +75,8 @@ commits for more info.
 - **$location** now uses `'!'` as the default hash-prefix for hash-bang URLs, instead of the empty
   string. ([Details](guide/migration#commit-aa077e8))
 
-- **$compile** will (by default) not pre-assign bindings on controller instances.
-  ([Details](guide/migration#commit-bcd0d4))
+- **$compile** will (by default) not pre-assign bindings on component/directive controller
+  instances. ([Details](guide/migration#commit-bcd0d4))
 
 - **http** imposes additional restrictions to **JSONP** requests for security reasons
   (see [details](guide/migration#migrate1.5to1.6-ng-services-$http) below):
@@ -412,14 +412,14 @@ if the option does not provide a value attribute.
 <major />
 <a name="commit-bcd0d4"></a>
 **Due to [bcd0d4](https://github.com/angular/angular.js/commit/bcd0d4d896d0dfdd988ff4f849c1d40366125858)**,
-pre-assigning bindings on controller instances is disabled by default. It is still possible to turn
-it back on, which should help during the migration. Pre-assigning bindings has been deprecated and
-will be removed in a future version, so we strongly recommend migrating your applications to not
-rely on it as soon as possible.
+pre-assigning bindings on component/directive controller instances is disabled by default, which
+means that they will no longer be available inside the constructors. It is still possible to turn it
+back on, which should help during the migration. Pre-assigning bindings has been deprecated and will
+be removed in a future version, so we strongly recommend migrating your applications to not rely on
+it as soon as possible.
 
 Initialization logic that relies on bindings being present should be put in the controller's
-`$onInit()` method, which is guaranteed to always be called _after_ the bindings have been
-assigned.
+`$onInit()` method, which is guaranteed to always be called _after_ the bindings have been assigned.
 
 Before: