Fix Gtk-CRITICAL assertions creating noise and occasional lag in Linux/GTK (#11897)

* Fix Gtk-Critical assertion in PresetComboBoxes

Resolve the `gtk_cell_layout_get_cells: assertion GTK_IS_CELL_LAYOUT
failed` error by switching from `gtk_cell_layout_get_cells()` to
`gtk_container_get_children()` with direct PangoLayout ellipsization
on GtkEntry widgets.

Picked from PrusaSlicer:
https://github.com/prusa3d/PrusaSlicer/commit/e855ab5d

* Add defensive guards for GTK widget sizing

Fix Gtk-CRITICAL assertions in TextInput and DropDown widgets that
occur when the widget attempt relative sizing against window size
before GTK completes the window layout.

Changes include:
- TextInput.cpp: Clamp textSize.x >= -1 to prevent
  `gtk_widget_set_size_request` failures.
  - Picked from Prusa Slicer:
    https://github.com/prusa3d/PrusaSlicer/commit/e855ab5d
- DropDown.cpp: Guard against zero/negative dimensions during early
  initialization:
  - Prevent szContent.x = 0 when parent size is unavailable.
    - Unique to OrcaSlicer
    - Triggers during initializing DesignerPanel --> BasicInfo -->
      License DropDown before a parent size is available.
    - Latent bug exists in Bambu Studio, but Bambu does not have
      License field enabled on this panel.
    - Created global guard for future resilience.
  - Clamp szContent.y >= 1 for dropdowns before content initialized.
    - Bug exists in BambuStudio
    - Prusa did not implement the "ENH: ComboBox Second DropDown"

src/slic3r/GUI/Widgets/TextInput.cpp

@@ -197,6 +197,7 @@ void TextInput::DoSetSize(int x, int y, int width, int height, int sizeFlags)
     if (text_ctrl) {
         wxSize textSize = text_ctrl->GetSize();
         textSize.x = size.x - textPos.x - labelSize.x - 10;
+        if(textSize.x < -1) textSize.x = -1;
         text_ctrl->SetSize(textSize);
         text_ctrl->SetPosition({textPos.x, (size.y - textSize.y) / 2});
     }