Add support for text truncation to egui::Style (#4556)

* Closes #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.

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui_demo_app/src/backend_panel.rs

@@ -180,7 +180,7 @@ fn integration_ui(ui: &mut egui::Ui, _frame: &mut eframe::Frame) {
 
     #[cfg(target_arch = "wasm32")]
     ui.collapsing("Web info (location)", |ui| {
-        ui.style_mut().wrap = Some(false);
+        ui.style_mut().wrap_mode = Some(egui::TextWrapMode::Extend);
         ui.monospace(format!("{:#?}", _frame.info().web_info.location));
     });