Pause and PLR refinements

- Move `pause_print` argument `unload_length` after `show_lcd` so it's next to `DXC_ARGS`.
- Tweak the position and conditions of PLR save in `resume_print`.
- Add `Nozzle::park_mode_0_height` accessor to get the raised Z height.
- Remove extraneous `recovery.save` from `dwin.cpp`.
- Move PLR `info.volumetric...` to `flag`.
- Remove some G-code spaces in PLR code
- Document `pause.h` function declarations.

Marlin/src/libs/nozzle.h

@@ -83,6 +83,7 @@ class Nozzle {
 
   #if ENABLED(NOZZLE_PARK_FEATURE)
 
+    static float park_mode_0_height(const_float_t park_z) _Os;
     static void park(const uint8_t z_action, const xyz_pos_t &park=NOZZLE_PARK_POINT) _Os;
 
   #endif