Format Bar does not revert to settings when not overridden by .editorconfig

### What Happened?

After editing a document where a tab width of "2" was set in `.editorconfig` (e.g. an .xml file) when switching to a file with no tab width was specified in `.editorconfig`, the tab width remained at "2" even though the app default setting was "4" (as determined by the value of `io.elementary.code.settings.indent-width`.

### Steps to Reproduce

1. Open a project whose `.editorconfig` file has no global specification for `tab_width` (e.g. Code itself)
2. Open an XML file and e.g. the `.editorconfig` file
3. Focus the XML document - the format button becomes insensitive with a value of "2" as expected
4. Focus the other file - the format button becomes sensitive, as expected, but the value remains at "2"

### Expected Behavior

Where the `editorconfig` does not specify a tab width for a file type, then the app default setting should be used if the file is empty or has no tab width set internally; if the file has a tab_width specified in its header or otherwise then that should be used. This should occur regardless of the previously focussed document.

### OS Version

7.x (Early Access)

### Software Version

Latest release (I have run all updates)

### Log Output

_No response_

### Hardware Info

_No response_

まず、再現手順にある XML ファイルと .editorconfig ファイルを使い、Format Bar のタブ幅の状態を .editorconfig の処理と併せて追跡します。ファイル間でフォーカスが移動したときに io.elementary.code.settings.indent-width 設定を確認します。未指定の tab_width が、ファイルに独自の tab_width がない場合にアプリのデフォルトへ戻れば完了です。

索引モデルが issue の本文から書いたものです。