chore: add .editorconfig for cross-editor consistency

Matches existing oxfmt settings (2-space indent, LF, UTF-8).
Ensures consistent formatting defaults for non-VS Code editors.

Fixes #11073

.editorconfig

@@ -0,0 +1,12 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.md]
+trim_trailing_whitespace = false