Add more folders to the list of ignored content dirs (#17892)

Closes #15452

This PR adds more directories to the list of ignored content dirs. These
are now handled the same as `node_modules`:

- Contents of this directory are ignored by default to avoid scanning
dependency trees
- Explicit `@import`s inside these folders are now treated as
_external_, bypassing any `.gitignore` files.

The new extensions are:

- Version control systems: `.hg`, `.svn`
- Bundler caches: `.venv`, `venv`, `.yarn`
- Framework caches: `.next`, `.turbo`, `.parcel-cache`, `__pycache__`,
`.svelte-kit`

## Test plan

Verified with the repro of #15452 by renaming the ignored directory to
`.venv` and installing a local tarball:

<img width="1283" alt="Screenshot 2025-05-06 at 13 14 55"
src="https://github.com/user-attachments/assets/3265acbb-e121-47b3-ac6c-e174770f8234"
/>

CHANGELOG.md

@@ -40,6 +40,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Upgrade: Don't add `-` to variants starting with `@` ([#17814](https://github.com/tailwindlabs/tailwindcss/pull/17814))
 - Upgrade: Don't format stylesheets that didn't change when upgrading ([#17824](https://github.com/tailwindlabs/tailwindcss/pull/17824))
 
+### Changed
+
+- Ignore `.hg`, `.svn`, `.venv`, `venv`, `.yarn`, `.next`, `.turbo`, `.parcel-cache`, `__pycache__`, and `.svelte-kit` folders by default (can be overridden by `@source …` rules) ([#17892](https://github.com/tailwindlabs/tailwindcss/pull/17892))
+- `@source` rules that point inside `.hg`, `.svn`, `.venv`, `venv`, `.yarn`, `.next`, `.turbo`, `.parcel-cache`, `__pycache__`, and `.svelte-kit` folders no longer consider your `.gitignore` rules ([#17892](https://github.com/tailwindlabs/tailwindcss/pull/17892))
+
 ## [4.1.4] - 2025-04-14
 
 ### Added

crates/oxide/src/scanner/fixtures/ignored-content-dirs.txt

@@ -1,2 +1,12 @@
 .git
+.hg
+.svn
 node_modules
+.yarn
+.venv
+venv
+.next
+.turbo
+.parcel-cache
+__pycache__
+.svelte-kit