add configure option to inferNamedImports

### Clear and concise description of the problem

For monorepo projects, it is likely that both `react` and preact `packages` required in the dependencies, so passing `resolveImport('preact', root)` may be problematic

### Suggested solution

add configure option

### Alternative

yarn patch

```diff
diff --git a/dist/imports.js b/dist/imports.js
index 8f16352ab74f329dd01389d416059754bbf0a99f..418fc1b9b83b7111799c2fe4acd7564ba351df75 100644
--- a/dist/imports.js
+++ b/dist/imports.js
@@ -42,9 +42,7 @@ function assertImportExists(name, cwd) {
}
exports.assertImportExists = assertImportExists;
function inferNamedImports(root) {
- return resolveImport('preact', root)
- ? { preact: ['h'], '@mdx-js/preact': ['mdx'] }
- : { react: 'React', '@mdx-js/react': ['mdx'] };
+ return { react: 'React', '@mdx-js/react': ['mdx'] };
}
exports.inferNamedImports = inferNamedImports;
//# sourceMappingURL=imports.js.map
\ No newline at end of file

```

### Additional context

Sorry for any mistakes. English is not my native language

The payload points to dist/imports.js and inferNamedImports, with resolveImport('preact', root) controlling the current inference. Trace how inferNamedImports is called and how its configuration could be supplied; done means the preact-versus-React choice is configurable without relying on the monorepo dependency lookup.

Written by the indexing model from the issue text.