Fix recursion when component with height-for-width items is in a FlexboxLayout

[dfaure-kdab]

Revert "FlexboxLayout: detect binding loops when components have height-for-width children (#11381)"

This reverts commit edf9800.

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Fix recursion when component with height-for-width items is in a FlexboxLayout

When a component containing Text with word-wrap or Image with aspect
ratio is placed inside a FlexboxLayout, evaluating the component's
vertical layout info would panic with recursion: layoutinfo-v →
internal layout → Text/Image reads width → component width → layout
cache → layoutinfo-v.

For builtins directly in a layout, the VTable cross_axis_constraint
parameter breaks this cycle. But for components, layoutinfo-v is a
property binding with no parameter mechanism.

Fix: add a cross-axis constraint thread-local in i_slint_core::layout.
Text and Image items check it when their explicit constraint is -1
(meaning "no constraint passed"). The thread-local is set at two
levels:

• Compiled path: SolveFlexboxLayout wraps its entire expression
  (including cells computation) with set_cross_axis_constraint
  (container_width), so all nested ImplicitLayoutInfo(Vertical, -1)
  calls inside components see the constraint.

• Interpreter path: get_layout_info_with_constraint saves/restores the
  thread-local at each component boundary, so nested components get
  the correct constraint for their level.