* clean up titlebar layout

* validating fix on macOS and re-adding comment

We compile using the alwaysStrict flag so these directives are not needed

Introduced in  f95965a8 Just assume zero size if element is undefined

fixes #56273
fixes #55438

This ensures that e.g. clicking into an iframe of a <webview> does not accidentally trigger blur events with upcoming Electron 3.0.x

#57130

fixes #57130

fixes #55886

* merging menu/titlebar

* install empty native menu to override electron

* hacky fix #52522

* adding issue to comments

* addressing feedback

refs #52884

- avoid public modifier
- use Disposable where applicable
- fix some event handler leaks
- clean up some TODO@ben