Get the directory path that contains the current executable.
Returns index into out_buffer.
On Windows, the result is encoded as WTF-8. On other platforms, the result is an opaque sequence of bytes with no particular encoding.
pub fn executableDirPath(io: Io, out_buffer: []u8) ExecutablePathError!usize
pub fn executableDirPath(io: Io, out_buffer: []u8) ExecutablePathError!usize {
const n = try executablePath(io, out_buffer);
// Assert that the OS APIs return absolute paths, and therefore dirname
// will not return null.
return std.fs.path.dirname(out_buffer[0..n]).?.len;
}