* Part of https://github.com/zed-industries/community/issues/70

Allows to fully remove from Zed certain files or file groups: no items
will be scanned or added into worktrees, so nothing will be shown in
project tree, project search and go to file would not see those,
corresponding FS events will be ignored.

One exclusion is .git files: those are still not shown or accessible by
default, yet tracked in the worktrees.

By default, is configured to 
```json
  "file_scan_exclusions": [
    "**/.git",
    "**/.svn",
    "**/.hg",
    "**/CVS",
    "**/.DS_Store",
    "**/Thumbs.db",
    "**/.classpath",
    "**/.settings"
  ],
```

* In addition, contains code preparations for "search in included files"
feature: new SearchOptions variant, search crate and RPC adjustments

Release Notes:

- Added `file_scan_exclusions` section to project settings to completely
ignore certain files in Zed