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_

首先使用复现步骤中的 XML 和 .editorconfig 文件，跟踪 Format Bar 的制表符宽度状态以及 .editorconfig 的处理。焦点在文件之间移动时，检查 io.elementary.code.settings.indent-width 设置；当未指定的 tab_width 恢复为应用默认值（除非文件有自己的 tab_width）时，即表示完成。

由索引模型根据 Issue 内容生成。