fix(tsconfig): support node subpath imports in extends field

[gefydev]

Description

This PR fixes an issue where the `tsconfig` resolver fails to resolve Node subpath imports (specifiers starting with `#`) when used in the `extends` field.

Currently, `get_extended_tsconfig_path` falls back to `load_package_self_or_node_modules` for any specifier that does not start with `.` or `/`. This treats the `#` prefix as a literal directory name, leading to an unhandled `TsconfigNotFound` error.

Changes

• Added a new match arm for `Some(b'#')` in `get_extended_tsconfig_path`.
• Reused the existing `find_package_json_for_a_package` and `package_imports_resolve` methods to properly look up the closest `package.json` and resolve the subpath alias according to the Node specification.

Related Issues

Ref: rolldown/rolldown#9611

[Boshen]

closed by #1199