[rollup-plugin-typescript] Re-enable declarationDir outside output file/dir

[marekdedic]

• Rollup Plugin Name: rollup-plugin-typescript
• Rollup Plugin Version: 12.1.0
• Rollup Version: 4.22.4
• Operating System (or Browser): Ubuntu 22.04
• Node Version: 22.9.0
• Link to reproduction: marekdedic/rollup-plugin-htaccess/pull/121

Expected Behavior

Enable declarationDir to be outside the rollup output directory, much like it was possible in v11

Actual Behavior

Since v12, I get:

[!] (plugin typescript) RollupError: [plugin typescript] @rollup/plugin-typescript: Path of Typescript compiler option 'declarationDir' must be located inside the same directory as the Rollup 'file' option.

Additional Information

The change I'd like to be reconsidered was introduced in #1728. However, emitting declarations to a different place from the build output can be really useful for things like post-processing with api-extractor - having the intermediary declarations produced by rollup be outside the final output dir makes it much easier to not accidentally include these files in the final build.