Add an unsafe method view_mut_raw (#1850)

* adding .vscode folder to .gitignore

* Adding view_mut_raw to generated arrays

* test populating rust vector from JS  function

* Uint32Array test, need to make it generic

* Add doc + more test cases

* replacing macro-generated tests with generic test function

it is cleaner, safer and better that way

* improving rustdoc

crates/js-sys/tests/wasm/Array.js

@@ -0,0 +1,6 @@
+// Used for `Array.rs` tests
+exports.populate_array =  function(arr, start, len) {
+  for (i = 0; i < len; i++) {
+    arr[i] = start + i;
+  }
+};