Fix app.running field only being set if starting with app.Run()

[Jacalz]

Description:

This fixes the app.running field only being set if running with app.Run() and not when using window.ShowAndRun(), i.e. it was false for the majority of applications. The glfw driver already had a flag to check if it was running or not. The PR moves the running flag into the mobile driver and cleans up the one we already had in the glfw driver.

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

[coveralls]

coverage: 65.314% (-0.005%) from 65.319% when pulling bed11fa on Jacalz:init-cleanup-improved into b8234f7 on fyne-io:develop.

[Jacalz]

The plan was initially to apply a re-roll of 460fa8d but it felt better to work on that separately.

[andydotxyz]

In testing with fyne_demo closing it I get this panic:

panic: close of closed channel

goroutine 1 [running, locked to thread]:
fyne.io/fyne/v2/internal/driver/glfw.(*gLDriver).Quit(0x140001e5700?)
	/Users/andy/Code/Fyne/fyne/internal/driver/glfw/driver.go:110 +0xb4
fyne.io/fyne/v2/internal/driver/glfw.(*window).destroy(0x140005023c0, 0x140001e5700)
	/Users/andy/Code/Fyne/fyne/internal/driver/glfw/window.go:283 +0x60
fyne.io/fyne/v2/internal/driver/glfw.(*gLDriver).runGL(0x140001e5700)
	/Users/andy/Code/Fyne/fyne/internal/driver/glfw/loop.go:137 +0x53c
fyne.io/fyne/v2/internal/driver/glfw.(*gLDriver).Run(0x140001e5700)
	/Users/andy/Code/Fyne/fyne/internal/driver/glfw/driver.go:168 +0x80
fyne.io/fyne/v2/internal/driver/glfw.(*window).ShowAndRun(0x140005023c0)
	/Users/andy/Code/Fyne/fyne/internal/driver/glfw/window.go:227 +0x2c
main.main()
	/Users/andy/Code/Fyne/fyne/cmd/fyne_demo/main.go:68 +0x4b0
exit status 2

[Jacalz]

I haven't been able to replicate the crash but I pushed a commit that should solve it hopefully.