Several upstream-suitable improvements to the START_PRINT_FROM_Z
feature added in the previous commit.

Self-contained resume (no PLR dependency)
-----------------------------------------
The original implementation used PrintJobRecovery::info as a transport
to invoke the standard PLR resume() path. This made the feature depend
on POWER_LOSS_RECOVERY at compile time and waste flash on AVR boards
that didn't otherwise need PLR.

skip_to_z.cpp now performs the resume itself by enqueueing a small
sequence of g-codes:
  M140 S<bed>     (bed heat, async)
  M104 T<n> S<t>  (hotend heat, async, per tool)
  M190 S<bed>     (wait for bed)
  T<active>       (switch to active tool)
  M109 T<n> S<t>  (wait for active hotend)
  G20/G21, G90, M82, G28 X Y
  G92 E<scanned>  (restore extruder counter)
  G1 Z<scanned> F300
  G91 / M83       (restore relative modes if needed)
  M106 P<i> S<v>  (restore fan speeds)
Then card.setIndex() + card.startOrResumeFilePrinting().

SanityCheck no longer requires POWER_LOSS_RECOVERY.
M1005.cpp drops the powerloss.h include and the recovery.resume() call.
The Configuration_adv.h block is moved out of the POWER_LOSS_RECOVERY
section to a sibling block under HAS_MEDIA, with the comment updated
to reflect the new self-contained design.

Smarter target detection: extrusion-aware Z-establishing line
-------------------------------------------------------------
A Bricked-vase print would previously trigger on any move that crossed
the target Z, including parking/purge moves like 'G1 Z15 F500' that
have no extrusion at the target height. The scanner now:
  * Tracks the most recent line that established the current Z
    (saving the pre-line state and the line's byte offset).
  * Triggers only when an extrusion move (E increasing) occurs while
    Z >= target.
  * Resumes from the Z-establishing line so the printer travels to
    (X,Y,Z) before any extrusion. The state used for the resume is
    the snapshot taken BEFORE the Z-establishing line ran, with z
    overwritten to the actual current Z.

Live progress reporting
-----------------------
Long files on slow MCUs can take many seconds to scan. New
report_progress() helper (throttled to ~1 s) updates:
  * LCD status line: 'Scan Z 1.2/12.0 56%'
  * Serial host log: 'SkipToZ: 56% z=1.2/12.0 sdpos=12345'

Per-file action submenu (LCD)
-----------------------------
Previously the EDIT_ITEM 'Print from Z...' was at the top of the file
selector and was a global value applied to whichever file you next
selected. Now selecting a file opens a small action submenu:
  Cancel
  Print from Z: <value>   (0 = normal print)
  Print
which makes the per-file intent explicit and keeps the file list
uncluttered. The new submenu function menu_sd_file_action() lives in
menu_media.cpp behind ENABLED(START_PRINT_FROM_Z).

current_edit_value() accessor (menu.h)
--------------------------------------
MenuEditItemBase exposes a new public static getter for the address
of the variable currently being edited. This lets context-sensitive
input handling decide what action to take based on the field on
screen. Default-disabled menus pay no cost; the accessor inlines.

RIGHT button loads current Z (ADC keypad)
-----------------------------------------
On RRW keypads (ZONESTAR_LCD etc.) RIGHT historically clears the
edit value to zero. While editing target_z and Z is homed, RIGHT
now loads the current Z position (scaled to float52). For all other
edit fields and unhomed Z, behavior is unchanged.

features.ini
------------
Adds a build_src_filter for START_PRINT_FROM_Z so the new sources
are only compiled into builds that enable the feature. This avoids
linking skip_to_z.cpp + M1005.cpp into firmware that doesn't use
the feature.

Verified
--------
mega2560 builds cleanly both with and without START_PRINT_FROM_Z
(Flash 62.2 KB without -> 82.6 KB with).