Update PersistentStore api (#11538)

- Clean up the API to use a `static` class instance to adhere to Marlin convention
- Add `const` position data access for read/write
- Add Storage capacity to the interface

Marlin/src/module/configuration_store.h

@@ -24,6 +24,9 @@
 #define CONFIGURATION_STORE_H
 
 #include "../inc/MarlinConfig.h"
+#if ENABLED(EEPROM_SETTINGS)
+  #include "../HAL/persistent_store_api.h"
+#endif
 
 #define ADD_PORT_ARG ENABLED(EEPROM_CHITCHAT) && NUM_SERIAL > 1
 
@@ -96,11 +99,10 @@ class MarlinSettings {
 
       static bool eeprom_error, validating;
 
-      #if ENABLED(AUTO_BED_LEVELING_UBL) // Eventually make these available if any leveling system
-                                         // That can store is enabled
-        static constexpr uint16_t meshes_end = E2END - 128; // 128 is a placeholder for the size of the MAT; the MAT will always
-                                                            // live at the very end of the eeprom
-
+      #if ENABLED(AUTO_BED_LEVELING_UBL)  // Eventually make these available if any leveling system
+                                          // That can store is enabled
+        static const uint16_t meshes_end; // 128 is a placeholder for the size of the MAT; the MAT will always
+                                          // live at the very end of the eeprom
       #endif
 
       static bool _load(PORTINIT_SOLO);