Add support for text truncation to egui::Style

[abey79]

• Closes Style feature to have label truncate by default #4473

This PR introduce Style::wrap_mode, which adds support for text truncation in addition to text wrapping. This PR also update some width calculation of the ComboBox.

Core

• Add egui::TextWrapMode (pure enum with Extend, Wrap, Truncate)
• Add Style::wrap_mode: Option<tTextWrapMode>
• DEPRECATED: Style::wrap, use Style::wrap_mode instead.
• Add Ui::wrap_mode() to return the wrap mode to use in the current ui. If specified in Style, return it. Otherwise, return TextWrapMode::Wrap for vertical layout and wrapping horizontal layout, and TextWrapMode::Extend otherwise.
• DEPRECATED: Ui::wrap_text(), use Ui::wrap_mode instead.

Widget

• Update the width calculation of the ComboBox button (not its popup menu).
  • Now, ComboBox::width() (defaulting to Spacing::combo_width) is always considered a minimum width and will extend the Ui, regardless of the selected text width and wrap mode.
  • Introduce ComboBox::wrap_mode, which overrides Ui::wrap_mode for the selected text layout.
    • Note: since ComboBox uses ui.horizontal internally, the default wrap mode is always TextWrapMode::Extend, regardless of the caller's Ui's layout.
  • The ComboBox button no longer extend to ui.available_width() with wrapping is enabled.
  • BREAKING: ComboBox::wrap() no longer has a bool argument and is now a short-hand for ComboBox::wrap_mode(TextWrapMode::Wrap).
  • Added ComboBox::truncate() as short-hand for ComboBox::wrap_mode(TextWrapMode::Truncate).
• Update Label
  • Add Label::wrap_mode() to specify the text wrap mode.
  • BREAKING: Label::wrap() no longer has a bool argument and is now a short-hand for Label::wrap_mode(TextWrapMode::Wrap).
  • BREAKING: Label::truncate() no longer has a bool argument and is now a short-hand for Label::wrap_mode(TextWrapMode::Truncate).
• Update Button
  • Add Button::wrap_mode() to specify the text wrap mode.
  • BREAKING: Button::wrap() no longer has a bool argument and is now a short-hand for Button::wrap_mode(TextWrapMode::Wrap).
  • Added Button::truncate() as short-hand for Button::wrap_mode(TextWrapMode::Truncate).

Low-level

• BREAKING: WidgetText::into_galley() now takes an Option<TextWrapMode> instead of a Option<bool> argument.
• BREAKING: WidgetText::into_galley_impl(() now takes a TextWrapping argument instead of wrap: bool and availalbe_width: f32 arguments.

[emilk]

Looks great!