Editor tab bar settings (#7356)

This PR is another step to tabless editing (#6424, #4963). It adds
support for tab bar settings that allow the user to change its placement
or to hide completely.

Configuraton:

```json
"tab_bar": {
  "show": true
}
```

Placemnet options are "top", "bottom" and "no".

This PR intentionally doesn't affect tab bars of other panes (Terminal
for instance) to keep code changes small. I guess we'll do the rest in
separate PRs.

Release Notes:

- Added support for configuring the editor tab bar (part of #6424,
#4963).

---------

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/workspace/src/item.rs

@@ -69,7 +69,7 @@ impl ClosePosition {
 pub struct ItemSettingsContent {
     /// Whether to show the Git file status on a tab item.
     ///
-    /// Default: true
+    /// Default: false
     git_status: Option<bool>,
     /// Position of the close button in a tab.
     ///