Uri.isUri return type is problematic

[joaomoreno]

https://github.com/Microsoft/vscode/blob/fe9539a05ffb89bea781e7a4e7f7029980b30686/src/vs/base/common/uri.ts#L100

The return type of Uri.isUri being uri is Uri is problematic since it can have us write code like this:

const obj = { authority: '', fragment: '', path: '', query: '', scheme: '' };
if (isUri(obj)) {
  console.log(obj.fsPath.length);
}

TypeScript will gladly compile this without errors, yet the end result will be an NPE.

We should change that return type to simply boolean.

[jrieken]

good catch