settings: Add Sapling directory to default `file_scan_exclusions` (#45837)

Cory Wilhite created 

[Sapling](https://sapling-scm.com/docs/git/git_support_modes/) is
similar to git / hg / jj in that it creates a /.sl directory when
initializing a repository. This can be added alongside the other source
control scan exclusions

includes a docs update for these defaults

Release Notes:
- Settings: Add Sapling directory to default `file_scan_exclusions`

Change summary

assets/settings/default.json | 1 +
docs/src/configuring-zed.md  | 2 ++
2 files changed, 3 insertions(+)

Detailed changes

docs/src/configuring-zed.md 🔗 

@@ -1923,6 +1923,8 @@ The result is still `)))` and not `))))))`, which is what it would be by default
   "**/.svn",
   "**/.hg",
   "**/.jj",
+  "**/.sl",
+  "**/.repo",
   "**/CVS",
   "**/.DS_Store",
   "**/Thumbs.db",