Fix crash on Ctrl+X with multiple carets in TextEdit

[Jordyfel]

Fix #81535 fix #83826

The crash was caused by this function occasionally leaving behind a caret with an invalid column index (larger than the column length), which caused a crash in an unrelated function. The fix is thus to clamp the caret index after cutting to the length of the new column.

However, the function has other problems. It's iteration is broken, since the backspace() call would remove carets during iteration, resulting in invalid index errors. So I changed the logic a little while trying to preserve the previous functionality. Also handled multiple carets accumulating on the same line after cutting, only one per line will remain now.

To reproduce a broken case fixed by this that doesn't cause a crash set two carets on one line, one on the line after it, and press Ctrl+X.

[kitbdev]

There is a crash when cutting and there is only one line.
Stacktrace:

godot.windows.editor.dev.x86_64.exe!CowData<TextEdit::Text::Line>::get(int p_index) Line 158 (c:\Projects\godotsrc\godot\core\templates\cowdata.h:158)
godot.windows.editor.dev.x86_64.exe!Vector<TextEdit::Text::Line>::operator[](int p_index) Line 96 (c:\Projects\godotsrc\godot\core\templates\vector.h:96)
godot.windows.editor.dev.x86_64.exe!TextEdit::Text::operator[](int p_line) Line 145 (c:\Projects\godotsrc\godot\scene\gui\text_edit.cpp:145)
godot.windows.editor.dev.x86_64.exe!TextEdit::_cut_internal(int p_caret) Line 6719 (c:\Projects\godotsrc\godot\scene\gui\text_edit.cpp:6719)
godot.windows.editor.dev.x86_64.exe!TextEdit::cut(int p_caret) Line 3720 (c:\Projects\godotsrc\godot\scene\gui\text_edit.cpp:3720)
godot.windows.editor.dev.x86_64.exe!TextEdit::gui_input(const Ref<InputEvent> & p_gui_input) Line 2136 (c:\Projects\godotsrc\godot\scene\gui\text_edit.cpp:2136)
godot.windows.editor.dev.x86_64.exe!CodeEdit::gui_input(const Ref<InputEvent> & p_gui_input) Line 568 (c:\Projects\godotsrc\godot\scene\gui\code_edit.cpp:568)
godot.windows.editor.dev.x86_64.exe!Control::_call_gui_input(const Ref<InputEvent> & p_event) Line 1811 (c:\Projects\godotsrc\godot\scene\gui\control.cpp:1811)
godot.windows.editor.dev.x86_64.exe!Viewport::_gui_input_event(Ref<InputEvent> p_event) Line 2236 (c:\Projects\godotsrc\godot\scene\main\viewport.cpp:2236)
godot.windows.editor.dev.x86_64.exe!Viewport::push_input(const Ref<InputEvent> & p_event, bool p_local_coords) Line 3327 (c:\Projects\godotsrc\godot\scene\main\viewport.cpp:3327)
godot.windows.editor.dev.x86_64.exe!Window::_window_input(const Ref<InputEvent> & p_ev) Line 1559 (c:\Projects\godotsrc\godot\scene\main\window.cpp:1559)
godot.windows.editor.dev.x86_64.exe!call_with_variant_args_helper<Window,Ref<InputEvent> const &,0>(Window * p_instance, void(Window::*)(const Ref<InputEvent> &) p_method, const Variant * * p_args, Callable::CallError & r_error, IndexSequence<0> __formal) Line 303 (c:\Projects\godotsrc\godot\core\variant\binder_common.h:303)
godot.windows.editor.dev.x86_64.exe!call_with_variant_args<Window,Ref<InputEvent> const &>(Window * p_instance, void(Window::*)(const Ref<InputEvent> &) p_method, const Variant * * p_args, int p_argcount, Callable::CallError & r_error) Line 418 (c:\Projects\godotsrc\godot\core\variant\binder_common.h:418)
godot.windows.editor.dev.x86_64.exe!CallableCustomMethodPointer<Window,Ref<InputEvent> const &>::call(const Variant * * p_arguments, int p_argcount, Variant & r_return_value, Callable::CallError & r_call_error) Line 99 (c:\Projects\godotsrc\godot\core\object\callable_method_pointer.h:99)
godot.windows.editor.dev.x86_64.exe!Callable::callp(const Variant * * p_arguments, int p_argcount, Variant & r_return_value, Callable::CallError & r_call_error) Line 58 (c:\Projects\godotsrc\godot\core\variant\callable.cpp:58)
godot.windows.editor.dev.x86_64.exe!Callable::call<Ref<InputEvent>>(Ref<InputEvent> <p_args_0>) Line 850 (c:\Projects\godotsrc\godot\core\variant\variant.h:850)
godot.windows.editor.dev.x86_64.exe!DisplayServerWindows::_dispatch_input_event(const Ref<InputEvent> & p_event) Line 2716 (c:\Projects\godotsrc\godot\platform\windows\display_server_windows.cpp:2716)
godot.windows.editor.dev.x86_64.exe!DisplayServerWindows::_dispatch_input_events(const Ref<InputEvent> & p_event) Line 2686 (c:\Projects\godotsrc\godot\platform\windows\display_server_windows.cpp:2686)
godot.windows.editor.dev.x86_64.exe!Input::_parse_input_event_impl(const Ref<InputEvent> & p_event, bool p_is_emulated) Line 731 (c:\Projects\godotsrc\godot\core\input\input.cpp:731)
godot.windows.editor.dev.x86_64.exe!Input::flush_buffered_events() Line 995 (c:\Projects\godotsrc\godot\core\input\input.cpp:995)

Otherwise this fixes the crash.

Another issue is cutting a folded line puts the caret on a hidden line.

Some minor issues that can be fixed in a separate PR:

• The caret's visual column isn't the kept same on non fixed-width text, or on the last line.
• Undoing a cut on an tabbed line moves the caret.
• Cutting a wrapped line and undoing puts the caret on the first line wrap if there is only one caret.

And btw both indexes and indices are correct spellings.

[Jordyfel]

Thank you for the review!

Fixed the crash on only one line, handled hidden lines, and fixed the logic for preserving the visually perceived caret column.

[akien-mga]

Superseded by #86978.