Fix std::format type mismatch mixing std::wstring and std::string

[benhillis]

Problem

In WSLCContainer::Create(), the bind source path for file mounts is constructed using std::format with a narrow format string but passing sourceFilename (std::wstring) alongside parentVMPath (std::string).

std::format with a narrow format string does not accept std::wstring arguments in standard C++20. This is a type mismatch that could cause compilation failures or undefined behavior.

Fix

Convert sourceFilename from std::wstring to std::string via WideToMultiByte() before passing it to std::format, consistent with how the codebase handles wide-to-narrow conversions elsewhere.

Testing

Type-correctness fix in the volume bind path construction for file mounts (introduced in #40137).

[Copilot]

Pull request overview

Fixes a C++20 std::format argument type mismatch in the WSLC container create path by ensuring wide strings aren’t passed to a narrow format string when constructing Docker bind mount sources.

Changes:

• Convert sourceFilename (std::wstring) to UTF-8 std::string via wsl::shared::string::WideToMultiByte() before using it in std::format.
• Keep the bind source construction logic unchanged for directory mounts (no filename suffix).