Fixes#20416 for Oxfmt
- Gate `vite.config.ts` recognition behind `VP_VERSION` env var
- With it, only vite.config.ts is recognized
- Without it, excluded from config candidates (.oxfmtrc.json, oxfmt.config.ts are used)
- Refactor JS config loader into `loadJsConfig` / `loadVitePlusConfig` with shared `importJsConfig` helper
- `loadVitePlusConfig` should be updated to use `resolveConfig` from `vite-plus` soon
- Split tests into `vite_config` (non VP mode) and `vite_plus` (VP mode)
Current status:
- oxfmt: #20326 was merged
- oxlint: After discussion in #20327, it was decided NOT to merge
First, correct this inconsistency.
Since #20326 includes a change that displays errors from the JS side as-is, we will keep that part.
If oxfmt.config.ts fails to load, it is the user's responsibility, so reporting it as an error is correct.
However, this does not apply to vite.config.ts, so we ignore it.
Also refactored to report error message from JS.
NOTE: I'll do a self-review and add the test tomorrow.
<details>
<summary>Prompt</summary>
```
# Support `vite.config.*` as a Configuration File
## Target Files
- `vite.config.ts`
- `vite.config.mts`
- `vite.config.cts`
- `vite.config.js`
- `vite.config.mjs`
- `vite.config.cjs`
## Auto-Discovery Priority
When searching for a config file from `cwd` upwards, the following priority applies within the same directory:
1. Tool-specific JSON/JSONC config files (e.g. `.oxfmtrc.json`, `.oxlintrc.json`)
2. Tool-specific JS/TS config files (e.g. `oxfmt.config.ts`, `oxlint.config.ts`)
3. `vite.config.*`
## Extracting Configuration
The default export of `vite.config.*` is expected to contain tool-specific configuration under a dedicated field:
- oxfmt: `.fmt`
- oxlint: `.lint`
If the field does not exist, an error is returned (e.g. `Expected a 'fmt' field in the default export.`).
## Explicit `--config` Flag
When `--config vite.config.ts` is explicitly specified, the same behavior applies. The file name is used to determine whether to extract a nested field.
## LSP
`vite.config.*` files are added to the file watch patterns so that configuration changes trigger a reload.
```
</details>
renovate[bot]