[WasmFS] Fix argument name for open in the Node backend. NFC

[kleisauke]

Split out from #24733.

[sbc100]

Isn't mode the correct name for the string arguments like w+ etc? i.e. its a string which matches FILE *fdopen(int fd, const char *mode); so mode makes sense to me.

[kleisauke]

I tried to follow Node.js conventions here:
https://nodejs.org/api/fs.html#fsopensyncpath-flags-mode

At first, I wondered "Why is mode being passed to flags?" and made this change to prevent that confusion.

[sbc100]

Ok.. well thats confusing. C calls the r/w/a string things mode.. not flags, but node calls is falgs. I guess maybe worth adding a comment for this.

[kleisauke]

It's a bit confusing indeed. I think it's only a issue with fs.open{sync,}() though, as that accepts flags (which can also be a number) and mode (corresponding to mode_t in native code).

emscripten/system/lib/libc/musl/src/fcntl/open.c

Lines 5 to 16 in 8e4eee8

	int open(const char *filename, int flags, ...)
	{
	mode_t mode = 0;
	if ((flags & O_CREAT) || (flags & O_TMPFILE) == O_TMPFILE) {
	va_list ap;
	va_start(ap, flags);
	mode = va_arg(ap, mode_t);
	va_end(ap);
	}
	int fd = __sys_open_cp(filename, flags, mode);

As possible follow-up, perhaps we could do?:

Suggested change

	[[nodiscard]] int _wasmfs_node_open(const char* path, const char* flags);
	[[nodiscard]] int _wasmfs_node_open(const char* path, int flags);

That would make it less confusing, as it would align with POSIX open(2) (and would avoid the need of UTF8ToString()).

[kleisauke]

... actually, we can't change const char* flags to int flags as Node.js's fs.constants are derived from the underlying file system constants, which can vary.