monaco-editor: Find model by resource in SimpleEditorModelResolverService

[spahnke]

This PR fixes microsoft/monaco-editor#935

Currently, if you run the following code in the Monaco Playground and use "Peek Definition", or "Peek References" on the method next() in line 3, you get the error "Model not found" on the browser console. This is because the SimpleEditorModelResolverService only takes into account the currently attached model. This PR instead searches through all models.

const lib = `declare class Facts {
	/**
	 * Returns the next fact
	 *
	 * [Online documentation](http://www.google.de)
	 */
	static next(): string;
}`;

const uri = monaco.Uri.file("filename/facts.d.ts");
monaco.languages.typescript.javascriptDefaults.addExtraLib(lib, uri.toString());
monaco.editor.createModel(lib, "typescript", uri);

monaco.editor.create(document.getElementById("container"), {
    value: `class Chuck {
    greet() {
        return Facts.next();
    }
}`,
    language: "javascript"
});

Thanks!

[alexdima]

👍 Thank you!