Incompatibility between WindowsAppRuntime.dll and SetDefaultDllDirectories

@DrusTheAxe is already working on this.

Since Feb 24, 2025.

### Describe the bug

Hello, we are using WindowsAppRuntime (indirectly) from an winui3 desktop application. We noticed that the application does not start when calling [SetDefaultDllDirectories](https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-setdefaultdlldirectories). I managed to track the issue to [this](https://github.com/microsoft/WindowsAppSDK/blob/v1.5.3/dev/UndockedRegFreeWinRT/catalog.cpp#L50) LoadLibraryExW call when calling it with a relative path (`dcompi.dll` during my tests)
).

The documentation of LoadLibraryExW states about `LOAD_WITH_ALTERED_SEARCH_PATH` that:
> If this value is used and lpFileName specifies a relative path, the behavior is undefined.

A minimally reproducible example of the behavior (without the entire winui infrastructure, just for demonstration purposes):
```
int main()
{
SetDefaultDllDirectories(LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);
HMODULE mod = LoadLibraryExW(L"dcompi.dll", nullptr, LOAD_WITH_ALTERED_SEARCH_PATH);
return 0;
}
```

### Steps to reproduce the bug

Run any WindowsAppRuntime app that calls SetDefaultDllDirectories. It should just work.

### Expected behavior

_No response_

### Screenshots

_No response_

### NuGet package version

None

### Packaging type

_No response_

### Windows version

_No response_

### IDE

Visual Studio 2022

### Additional context

_No response_