Return impl IntoElement in Render and RenderOnce traits (#3839)

- Returning `IntoElement` because it's more universal than `Element` and
allows us to easily return components.
- Using `impl IntoElement` in `RenderOnce` for consistency, which
requires `Component` to allocate an `AnyElement`. We use a bump
allocated arena anyway for these, and my benchmark doesn't show an
impact.


![frame-time-histogram](https://github.com/zed-industries/zed/assets/1789/d3889cca-9ebc-4d72-aa68-34a5be3bad3c)

In this histogram, frames-0 is this PR, frames-1 is main.

Release Notes:

- N/A

crates/editor2/src/editor.rs

@@ -9287,7 +9287,7 @@ impl FocusableView for Editor {
 }
 
 impl Render for Editor {
-    fn render<'a>(&mut self, cx: &mut ViewContext<'a, Self>) -> impl 'static + Element {
+    fn render<'a>(&mut self, cx: &mut ViewContext<'a, Self>) -> impl IntoElement {
         let settings = ThemeSettings::get_global(cx);
         let text_style = match self.mode {
             EditorMode::SingleLine | EditorMode::AutoHeight { .. } => TextStyle {