Fix, improve Power Loss Recovery (#13703)

- Save and restore workspace offsets
- Add retract and purge (hidden) options
- Always restore axis relative modes
- Use added `G92.9` to do position restores

Marlin/src/feature/power_loss_recovery.h

@@ -35,6 +35,8 @@
 #define SAVE_INFO_INTERVAL_MS 0
 //#define SAVE_EACH_CMD_MODE
 //#define DEBUG_POWER_LOSS_RECOVERY
+#define POWER_LOSS_PURGE_LEN 20
+#define POWER_LOSS_RETRACT_LEN 10
 
 typedef struct {
   uint8_t valid_head;
@@ -42,6 +44,13 @@ typedef struct {
   // Machine state
   float current_position[NUM_AXIS];
 
+  #if HAS_HOME_OFFSET
+    float home_offset[XYZ];
+  #endif
+  #if HAS_POSITION_SHIFT
+    float position_shift[XYZ];
+  #endif
+
   uint16_t feedrate;
 
   #if HOTENDS > 1