Auto merge of #29279 - chansuke:chore/update-gitignore, r=mrobinson

Cleanup .gitignore

<!-- Please describe your changes on the following line: -->
Refactor editor related .gitignore.

ref:
https://github.com/github/gitignore/blob/main/Global/Emacs.gitignore
https://github.com/github/gitignore/blob/main/Global/Vim.gitignore
https://github.com/rust-lang/rust/blob/master/.gitignore

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because they simply change the `.gitignore` file.

.gitignore

@@ -28,29 +28,34 @@ Servo.app
 /glfw
 capture_webrender/
 /screenshots
-# Editors
 
-# IntelliJ
+# Editors
+## IntelliJ
 .idea
 *.iws
 *.iml
 
-#Gradle
+## Gradle
 .gradle
 
-# VSCode
+## VSCode
 .vscode
 !/.vscode/extensions.json
 !/.vscode/settings.json
 
-# Emacs
+## Emacs
 *~
-*#*
+.#*
+\#*
+\#*\#
+
+## Vim
+Session.vim
+Sessionx.vim
 
 /unminified-js
 
 # Hololens artifacts
-
 support/hololens/x64/
 support/hololens/ARM/
 support/hololens/ARM64/