Rollup merge of #81260 - vn971:restore-editorconfig, r=Mark-Simulacrum

Add .editorconfig

This adds a .editorconfig file to rust-lang/rust, matching Clippy's. It's not clear that this will benefit many people, but the cost is low and the rewards are potentially meaningful.

.editorconfig

@@ -13,6 +13,8 @@ indent_style = space
 indent_size = 4
 
 [*.md]
+# double whitespace at end of line
+# denotes a line break in Markdown
 trim_trailing_whitespace = false
 
 [*.yml]