Allow loading the main module via dlopen

[zebreus]

Calling dl_open with a NULL path now returns the handle of the main module. The PR also changes the dlopen handle of the main module to 1, because 0 means search everywhere.

Description

[Copilot]

Pull Request Overview

This PR allows the main module to be loaded via dlopen by handling a NULL file path argument and updating the main module handle from 0 to 1.

• Added a branch in dlopen to immediately return the main module handle when the path is NULL.
• Updated the main module handle constant and the next module handle allocation in the linker.
• Adjusted comments in both files to reflect the new handle values.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
lib/wasix/src/syscalls/wasix/dlopen.rs	Added a null check branch to return the main module handle immediately when dlopen is called with NULL.
lib/wasix/src/state/linker.rs	Updated the main module handle from 0 to 1 and adjusted next_module_handle accordingly.

Comments suppressed due to low confidence (2)

lib/wasix/src/state/linker.rs:1016

• Ensure that the updated main module handle value (from 0 to 1) is adopted consistently across interfacing modules and update any related documentation if necessary.

            next_module_handle: MAIN_MODULE_HANDLE.0 + 1,

lib/wasix/src/syscalls/wasix/dlopen.rs:32

• Add unit tests for the null path branch to verify that calling dlopen with a NULL path returns the main module handle appropriately.

    if path.is_null() {

[Copilot]

[nitpick] Consider refactoring duplicated input string retrieval logic by extracting common functionality into a helper function to improve maintainability.

[promptless]

✅ No documentation updates required.

[Arshia001]

@zebreus we don't have the 'search all modules after the given handle' functionality; if you give dlopen a non-zero module handle, it'll look in that module only. It's likely whatever required this change will depend on that functionality as well. Otherwise, lgtm.