[TASK] Declare Fluid-based Page Module components internal

In order to stabilize this API, all APIs are marked
as internal in order to allow changes once Fluid-based
page module is stable enough to remove the info in
further patch-level releases.

Resolves: #91153
Releases: master
Change-Id: I26737e5ab89947fdcd7a0bf99c30310fce3b0a3a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64268


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Josef Glatz <josefglatz@gmail.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>

typo3/sysext/backend/Classes/View/BackendLayout/ContentFetcher.php

@@ -40,6 +40,8 @@ use TYPO3\CMS\Core\Utility\GeneralUtility;
  * - Capable of returning all records in active language as flat array
  * - Capable of returning records for a given column in a given (optional) language
  * - Capable of returning translation data (brief info about translation consistency)
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 class ContentFetcher
 {

typo3/sysext/backend/Classes/View/BackendLayout/Grid/AbstractGridObject.php

@@ -34,6 +34,8 @@ use TYPO3\CMS\Core\Utility\StringUtility;
  * @see GridColumn
  * @see GridColumnItem
  * @see LanguageColumn
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 abstract class AbstractGridObject
 {

typo3/sysext/backend/Classes/View/BackendLayout/Grid/Grid.php

@@ -32,6 +32,8 @@ namespace TYPO3\CMS\Backend\View\BackendLayout\Grid;
  *       - GridColumnItem (one per record)
  *
  * Accessed in Fluid templates.
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 class Grid extends AbstractGridObject
 {

typo3/sysext/backend/Classes/View/BackendLayout/Grid/GridColumn.php

@@ -34,6 +34,8 @@ use TYPO3\CMS\Core\Utility\GeneralUtility;
  * in the page layout.
  *
  * Accessed from Fluid templates.
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 class GridColumn extends AbstractGridObject
 {

typo3/sysext/backend/Classes/View/BackendLayout/Grid/GridColumnItem.php

@@ -36,6 +36,8 @@ use TYPO3\CMS\Core\Versioning\VersionState;
  * is-versioned, is-editable, is-delible and so on.
  *
  * Accessed from Fluid templates.
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 class GridColumnItem extends AbstractGridObject
 {

typo3/sysext/backend/Classes/View/BackendLayout/Grid/GridRow.php

@@ -24,6 +24,8 @@ namespace TYPO3\CMS\Backend\View\BackendLayout\Grid;
  * Is solely responsible for grouping GridColumns.
  *
  * Accessed in Fluid templates.
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 class GridRow extends AbstractGridObject
 {

typo3/sysext/backend/Classes/View/BackendLayout/Grid/LanguageColumn.php

@@ -38,6 +38,8 @@ use TYPO3\CMS\Core\Versioning\VersionState;
  *
  * Accessed from Fluid templates - generated from within BackendLayout when
  * "page" module is in "languages" mode.
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 class LanguageColumn extends AbstractGridObject
 {

typo3/sysext/backend/Classes/View/BackendLayout/RecordRememberer.php

@@ -19,6 +19,9 @@ namespace TYPO3\CMS\Backend\View\BackendLayout;
 
 use TYPO3\CMS\Core\SingletonInterface;
 
+/**
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
+ */
 class RecordRememberer implements SingletonInterface
 {
     /**

typo3/sysext/backend/Classes/View/Drawing/BackendLayoutRenderer.php

@@ -51,6 +51,8 @@ use TYPO3\CMS\Fluid\View\TemplateView;
  *
  * - Initializes the clipboard used in the page layout
  * - Inserts an encoded paste icon as JS which is made visible when clipboard elements are registered
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 class BackendLayoutRenderer
 {

typo3/sysext/backend/Classes/View/Drawing/DrawingConfiguration.php

@@ -29,6 +29,8 @@ use TYPO3\CMS\Core\Localization\LanguageService;
  * tt_content fields and CTypes.
  *
  * Corresponds to legacy public properties from PageLayoutView.
+ *
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
  */
 class DrawingConfiguration
 {

typo3/sysext/backend/Classes/View/PageLayoutContext.php

@@ -36,6 +36,9 @@ use TYPO3\CMS\Core\Site\SiteFinder;
 use TYPO3\CMS\Core\Type\Bitmask\Permission;
 use TYPO3\CMS\Core\Utility\GeneralUtility;
 
+/**
+ * @internal this is experimental and subject to change in TYPO3 v10 / v11
+ */
 class PageLayoutContext
 {
     /**