Environment information

CLI:
  Version:                      1.9.2
  Color support:                true

Platform:
  CPU Architecture:             x86_64
  OS:                           windows

Environment:
  BIOME_LOG_PATH:               unset
  BIOME_LOG_PREFIX_NAME:        unset
  BIOME_CONFIG_PATH:            unset
  NO_COLOR:                     unset
  TERM:                         unset
  JS_RUNTIME_VERSION:           "v22.6.0"
  JS_RUNTIME_NAME:              "node"
  NODE_PACKAGE_MANAGER:         "npm/10.8.3"

Biome Configuration:
  Status:                       Loaded successfully
  Formatter disabled:           false
  Linter disabled:              false
  Organize imports disabled:    false
  VCS disabled:                 true

Workspace:
  Open Documents:               0

### What happened?

1. Set up a project with `indent_size=3` in `.editorconfig` and a `.prettierrc.json` with no `tabWidth` set.
2. `npx @biomejs/biome migrate prettier`
3. `npx @biomejs/biome format --write`

Observe that the indentation changes on all files and that `biome.json` has both `formatter.indentWidth` 2 and `formatter.useEditorconfig` true.

### Expected result

Indentation should not change.

I'm thinking that `formatter.indent_size` should be omitted from `biome.json`, not defaulted to 2, when absent from `prettier` config.

### Code of Conduct

- [X] I agree to follow Biome's Code of Conduct