Remove wildcard imports (#5018)

<!--
Please read the "Making a PR" section of
[`CONTRIBUTING.md`](https://github.com/emilk/egui/blob/master/CONTRIBUTING.md)
before opening a Pull Request!

* Keep your PR:s small and focused.
* The PR title is what ends up in the changelog, so make it descriptive!
* If applicable, add a screenshot or gif.
* If it is a non-trivial addition, consider adding a demo for it to
`egui_demo_lib`, or a new example.
* Do NOT open PR:s from your `master` branch, as that makes it hard for
maintainers to test and add commits to your PR.
* Remember to run `cargo fmt` and `cargo clippy`.
* Open the PR as a draft until you have self-reviewed it and run
`./scripts/check.sh`.
* When you have addressed a PR comment, mark it as resolved.

Please be patient! I will review your PR, but my time is limited!
-->

I removed (I hope so) all wildcard imports I found.

For me on my pc this improved the build time:
- for egui -5s
- for eframe -12s

* [x] I have followed the instructions in the PR template

examples/custom_window_frame/src/main.rs

@@ -43,7 +43,7 @@ impl eframe::App for MyApp {
 }
 
 fn custom_window_frame(ctx: &egui::Context, title: &str, add_contents: impl FnOnce(&mut egui::Ui)) {
-    use egui::*;
+    use egui::{CentralPanel, UiBuilder};
 
     let panel_frame = egui::Frame {
         fill: ctx.style().visuals.window_fill(),
@@ -77,7 +77,7 @@ fn custom_window_frame(ctx: &egui::Context, title: &str, add_contents: impl FnOn
 }
 
 fn title_bar_ui(ui: &mut egui::Ui, title_bar_rect: eframe::epaint::Rect, title: &str) {
-    use egui::*;
+    use egui::{vec2, Align2, FontId, Id, PointerButton, Sense, UiBuilder};
 
     let painter = ui.painter();
 

examples/file_dialog/src/main.rs

@@ -86,7 +86,7 @@ impl eframe::App for MyApp {
 
 /// Preview hovering files:
 fn preview_files_being_dropped(ctx: &egui::Context) {
-    use egui::*;
+    use egui::{Align2, Color32, Id, LayerId, Order, TextStyle};
     use std::fmt::Write as _;
 
     if !ctx.input(|i| i.raw.hovered_files.is_empty()) {

examples/keyboard_events/src/main.rs

@@ -2,7 +2,7 @@
 #![allow(rustdoc::missing_crate_level_docs)] // it's an example
 
 use eframe::egui;
-use egui::*;
+use egui::{Key, ScrollArea};
 
 fn main() -> eframe::Result {
     env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).

examples/popups/src/main.rs

@@ -1,7 +1,7 @@
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
 #![allow(rustdoc::missing_crate_level_docs)] // it's an example
 
-use eframe::egui::*;
+use eframe::egui::{popup_below_widget, CentralPanel, ComboBox, Id, PopupCloseBehavior};
 
 fn main() -> Result<(), eframe::Error> {
     env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).