Update egui requirement from 0.17 to 0.18

[dependabot]

Updates the requirements on egui to permit the latest version.

Release notes

Sourced from egui's releases.

0.17.0 - Improved font selection and image handling

egui highlights:

• Use any-sized font
• Define custom text styles
• Easy image loading using new crate egui_extras

eframe highlights:

• glow is now the default renderer on both native on web
• follow OS light/dark mode preference

Full changelog: https://github.com/emilk/egui/blob/master/CHANGELOG.md

Changelog

Sourced from egui's changelog.

0.17.0 - 2022-02-22 - Improved font selection and image handling

Added ⭐

• Much improved font selection (#1154):
  • You can now select any font size and family using RichText::size amd RichText::family and the new FontId.
  • Easily change text styles with Style::text_styles.
  • Added Ui::text_style_height.
  • Added TextStyle::resolve.
  • Made the v-align and scale of user fonts tweakable (#1241).
• Plot:
  • Added Plot::x_axis_formatter and Plot::y_axis_formatter for custom axis labels (#1130).
  • Added Plot::allow_boxed_zoom(), Plot::boxed_zoom_pointer() for boxed zooming on plots (#1188).
  • Added plot pointer coordinates with Plot::coordinates_formatter (#1235).
  • Added linked axis support for plots via plot::LinkedAxisGroup (#1184).
• Context::load_texture to convert an image into a texture which can be displayed using e.g. ui.image(texture, size) (#1110).
• Ui::input_mut to modify how subsequent widgets see the InputState and a convenience method InputState::consume_key for shortcuts or hotkeys (#1212).
• Added Ui::add_visible and Ui::add_visible_ui.
• Added CollapsingHeader::icon to override the default open/close icon using a custom function. (1147).
• Added ui.data(), ctx.data(), ctx.options() and ctx.tessellation_options() (#1175).
• Added Response::on_hover_text_at_pointer as a convenience akin to Response::on_hover_text (1179).
• Opt-in dependency on tracing crate for logging warnings (#1192).
• Added ui.weak(text).
• Added Slider::step_by (1225).
• Added Context::move_to_top and Context::top_most_layer for managing the layer on the top (#1242).
• Support a subset of macOS' emacs input field keybindings in TextEdit (#1243).
• Added ability to scroll an UI into view without specifying an alignment (1247).
• Added Ui::scroll_to_rect (1252).

Changed 🔧

• ⚠️ Context::input and Ui::input now locks a mutex. This can lead to a dead-lock is used in an if let binding!
  • if let Some(pos) = ui.input().pointer.latest_pos() and similar must now be rewritten on two lines.
  • Search for this problem in your code using the regex if let .*input.
• Better contrast in the default light mode style (#1238).
• Renamed CtxRef to Context (#1050).
• Context can now be cloned and stored between frames (#1050).
• Renamed Ui::visible to Ui::is_visible.
• Split Event::Text into Event::Text and Event::Paste (#1058).
• Replaced Style::body_text_style with more generic Style::text_styles (#1154).
• TextStyle is no longer Copy (#1154).
• Replaced TextEdit::text_style with TextEdit::font (#1154).
• Plot::highlight now takes a bool argument (#1159).
• ScrollArea::show now returns a ScrollAreaOutput, so you might need to add .inner after the call to it (#1166).
• Replaced corner_radius: f32 with rounding: Rounding, allowing per-corner rounding settings (#1206).
• Replaced Frame's margin: Vec2 with margin: Margin, allowing for different margins on opposing sides (#1219).
• Renamed Plot::custom_label_func to Plot::label_formatter (#1235).
• Areas::layer_id_at ignores non-interatable layers (i.e. Tooltips) (#1240).
• ScrollAreas will not shrink below a certain minimum size, set by min_scrolled_width/min_scrolled_height (1255).
• For integrations:
  • Output has now been renamed PlatformOutput and Context::run now returns the new FullOutput (#1292).
  • FontImage has been replaced by TexturesDelta (found in FullOutput), describing what textures were loaded and freed each frame (#1110).

... (truncated)

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