Fix soft_wrap setting not applying to buffers starting with a different language (#25880)

Closes #22999 
# Problem

Currently, the default soft wrap mode of an editor is determined by
reading the language-specific settings of the language _at offset zero_
in the editor's (multi)buffer. While this provides a way to pick a
single soft wrap mode for a multi-language multibuffer, it's a bad
choice for a single-buffer multibuffer that begins with a different
embedded language. For example, Markdown with frontmatter:

```markdown
---
my_front_matter
---

# Hello World
```

Setting this in config:

```json
  "languages": {
    "Markdown": { "soft_wrap": "bounded" }
  },
```

Will not soft wrap the Markdown file as the language at offset zero is
YAML.

# Solution

Instead of using the language at offset zero, use the language of the
first buffer in the multibuffer (the buffer at offset zero). This gives
better behavior for single-buffer editors, and a similar default for
multi-language multibuffers as before.

# Testing

All existing `editor` crate tests pass, but I would appreciate any
guidance for where best to add additional testing.

Release Notes:

- Fixed soft_wrap setting not applying to buffers starting with a
different language

---------

Co-authored-by: Kirill Bulatov <kirill@zed.dev>

crates/vim/src/normal/paste.rs

@@ -160,7 +160,7 @@ impl Vim {
                     .buffer()
                     .read(cx)
                     .snapshot(cx)
-                    .settings_at(cursor_offset, cx)
+                    .language_settings_at(cursor_offset, cx)
                     .auto_indent_on_paste
                 {
                     editor.edit_with_block_indent(edits, original_start_columns, cx);