Migrate From V6 to V9

[suntong]

I was looking for migration guide but only found this, IE, from V8 to V9.

Following up on #869, I'm getting the following errors when migrating from V6 to V9:

undefined: app.Navigate
undefined: app.NewContextMenu
undefined: app.MenuItem
undefined: app.Reload
too many errors

and maybe more as I got too many errors at the end.

The reason I'm doing this is that I found a bunch of good go-app demos, but all in V6, like
https://github.com/maxence-charriere/go-app-demo/blob/v6/demo/server/main.go
and I was trying to make use of them in V9, but now it seems to be beyond me thus I'm asking for help.

[suntong]

• app.Navigate is fixed (How to do navigation in UI #869)
• app.Reload can be fixed same way (to ctx.Reload)

However, for app.MenuItem and app.NewContextMenu, I didn't find anything that is close in https://go-app.dev/reference