Enable the clippy::std_instead_of_core lint (#8394)

Prefer `core::` over `std::` where either work

* Part of https://github.com/emilk/egui/issues/5735

crates/eframe/src/web/app_runner.rs

@@ -344,7 +344,7 @@ impl AppRunner {
 
     /// Paint the results of the last call to [`Self::logic`].
     pub fn paint(&mut self) {
-        let clipped_primitives = std::mem::take(&mut self.clipped_primitives);
+        let clipped_primitives = core::mem::take(&mut self.clipped_primitives);
 
         if let Some(clipped_primitives) = clipped_primitives {
             let mut screenshot_commands = vec![];

crates/eframe/src/web/dropped_file.rs

@@ -1,8 +1,5 @@
-use std::{
-    future::Future,
-    path::{Path, PathBuf},
-    pin::Pin,
-};
+use core::{future::Future, pin::Pin};
+use std::path::{Path, PathBuf};
 
 #[derive(Debug)]
 pub(crate) struct WebFile {

crates/eframe/src/web/input.rs

@@ -32,7 +32,7 @@ pub fn primary_touch_pos(
     event: &web_sys::TouchEvent,
 ) -> Option<(egui::Pos2, web_sys::Touch)> {
     // On touchend we don't get anything in `touches`, but we still get `changed_touches`, so include those:
-    let all_touches: Vec<_> = std::iter::chain(
+    let all_touches: Vec<_> = core::iter::chain(
         (0..event.touches().length()).filter_map(|i| event.touches().get(i)),
         (0..event.changed_touches().length()).filter_map(|i| event.changed_touches().get(i)),
     )

crates/eframe/src/web/text_agent.rs

@@ -1,7 +1,8 @@
 //! The text agent is a hidden `<input>` element used to capture
 //! IME and mobile keyboard input events.
 
-use std::{cell::RefCell, rc::Rc};
+use core::cell::RefCell;
+use std::rc::Rc;
 
 use wasm_bindgen::prelude::*;
 
@@ -366,7 +367,7 @@ impl InputState {
         &self,
         text: &str,
         prefix_len_chars: usize,
-    ) -> Option<std::ops::Range<usize>> {
+    ) -> Option<core::ops::Range<usize>> {
         let selection_start = self.input.selection_start().unwrap_or(None)? as usize;
         let selection_end = self.input.selection_end().unwrap_or(None)? as usize;
 
@@ -444,7 +445,7 @@ impl InputState {
 }
 
 fn longest_common_prefix_length(a: &str, b: &str) -> usize {
-    std::iter::zip(a.chars(), b.chars())
+    core::iter::zip(a.chars(), b.chars())
         .take_while(|(a, b)| a == b)
         .count()
 }

crates/eframe/src/web/web_painter_wgpu.rs

@@ -368,7 +368,7 @@ impl WebPainter for WebPainterWgpu {
         // Submit the commands: both the main buffer and user-defined ones.
         render_state
             .queue
-            .submit(std::iter::chain(user_cmd_bufs, [encoder.finish()]));
+            .submit(core::iter::chain(user_cmd_bufs, [encoder.finish()]));
 
         if let Some((frame, capture_buffer)) = frame_and_capture_buffer {
             if let Some(capture_buffer) = capture_buffer

crates/eframe/src/web/web_runner.rs

@@ -1,4 +1,5 @@
-use std::{cell::RefCell, rc::Rc};
+use core::cell::RefCell;
+use std::rc::Rc;
 
 use wasm_bindgen::prelude::*;
 
@@ -107,7 +108,7 @@ impl WebRunner {
 
     fn unsubscribe_from_all_events(&self) {
         let events_to_unsubscribe: Vec<_> =
-            std::mem::take(&mut *self.events_to_unsubscribe.borrow_mut());
+            core::mem::take(&mut *self.events_to_unsubscribe.borrow_mut());
 
         if !events_to_unsubscribe.is_empty() {
             log::debug!("Unsubscribing from {} events", events_to_unsubscribe.len());
@@ -139,7 +140,7 @@ impl WebRunner {
 
     /// Returns `None` if there has been a panic, or if we have been destroyed.
     /// In that case, just return to JS.
-    pub(crate) fn try_lock(&self) -> Option<std::cell::RefMut<'_, AppRunner>> {
+    pub(crate) fn try_lock(&self) -> Option<core::cell::RefMut<'_, AppRunner>> {
         if self.panic_handler.has_panicked() {
             // Unsubscribe from all events so that we don't get any more callbacks
             // that will try to access the poisoned runner.
@@ -147,7 +148,7 @@ impl WebRunner {
             None
         } else {
             let lock = self.app_runner.try_borrow_mut().ok()?;
-            std::cell::RefMut::filter_map(lock, |lock| -> Option<&mut AppRunner> { lock.as_mut() })
+            core::cell::RefMut::filter_map(lock, |lock| -> Option<&mut AppRunner> { lock.as_mut() })
                 .ok()
         }
     }
@@ -158,9 +159,9 @@ impl WebRunner {
     /// and return `None` if this  runner has panicked.
     pub fn app_mut<ConcreteApp: 'static + App>(
         &self,
-    ) -> Option<std::cell::RefMut<'_, ConcreteApp>> {
+    ) -> Option<core::cell::RefMut<'_, ConcreteApp>> {
         self.try_lock()
-            .map(|lock| std::cell::RefMut::map(lock, |runner| runner.app_mut::<ConcreteApp>()))
+            .map(|lock| core::cell::RefMut::map(lock, |runner| runner.app_mut::<ConcreteApp>()))
     }
 
     /// Convenience function to reduce boilerplate and ensure that all event handlers