WasmPackage should have a constructor with an optional FileReader

[krisbitney]

The current WasmPackage constructor looks like this:

pub fn new(
        file_reader: Arc<dyn FileReader>,
        manifest: Option<Vec<u8>>,
        wasm_module: Option<Vec<u8>>,
    ) -> Self
    
// example usage
WasmPackage::new(
    Arc::new(SimpleFileReader::new()),
    wrap_info().ok(),
    wrap_wasm().ok()
)

It would be good for UX to have one that requires manifest and wasm_module, allowing the FileReader to be assigned a default. The default FileReader could be the SimpleFileReader from the core.

pub fn new(
        manifest: Vec<u8>,
        wasm_module: Vec<u8>,
    ) -> Self

// example usage
WasmPackage::new(
    wrap_info().ok().unwrap(),
    wrap_wasm().ok().unwrap(),
)