fix: prevent dash icon teardown crashes

[mihaly044]

Summary

Prevent GNOME Shell from aborting when a transient application item is removed from the hidden Dash2Dock Lite Dash.

Fixes the teardown path reported in #299 on GNOME 49/50.

Root cause

The crash is the Clutter invariant failure:

clutter_actor_destroy_all_children:
assertion failed: (self->priv->n_children < prev_n_children)

A diagnostic Dash subclass recorded the active redisplay path in shared memory. At the crash it was left at custom begin 21, proving that the failing dash.js:77 → dash.js:788 stack belonged to the extension-created Dash rather than the overview Dash.

Inspection of the fresh core resolved the recursive actor chain as:

DashIcon → StWidget → BaseIcon → StBoxLayout → StBin → StIcon

The assertion fired in the StBin that owns the BaseIcon texture. Dash2Dock Lite made that nested GNOME-owned StIcon reactive and hover-tracked. Removing a transient app while its texture was under pointer input could therefore drive a hover/style refresh while the BaseIcon subtree was being destroyed, allowing the icon bin child to be refreshed during destroy_all_children().

Changes

• Keep input on the owning AppIcon or Show Apps toggle button instead of the nested texture.
• Leave GNOME-owned inner StIcon textures non-reactive and not hover-tracked.
• Stop overriding Show Apps button reactivity and toggle state.
• Do not force private icon-texture creation during icon discovery.
• Do not attach teardown callbacks to nested StIcon actors.
• Treat Dash labels as borrowed references and stop removing GNOME-owned separators.

The magnification renderer, favorites, running indicators, and dock layout remain unchanged.

Verification

Tested on Fedora 44, GNOME Shell 50.3, Wayland, Dash2Dock Lite v100.

Before the final fix:

• Reproduced two GNOME Shell SIGABRT crashes in the VM.
• The original stress workload crashed at cycle 70.
• A Showtime-heavy workload with dock hover/click input crashed at cycle 5 of 200.

After the fix, using the same Showtime-heavy workload and pointer pattern:

• Completed 200 of 200 cycles with Shell PID 1371 unchanged and zero new cores.
• Completed a second 80 of 80 cycles with the same Shell PID and zero new cores.
• Verified the Show Apps button opens the application grid.
• Verified normal dock activation by launching Firefox.
• Found no Clutter assertion, disposed-object error, JS error, or TypeError in either test journal.
• Passed node --check and git diff --check.

This is related to, but distinct from, #336, which reports a null icon during _adjustIconSize().