Mouse Back Button should navigate back a page

[DHowett]

originally filed by @zadjii-msft

Press the mouse back button, we should go back. I forget which VKEY that is. Probably should be handled kinda like backspace, where back on the main page doesn't actually dismiss the palette

[lauren-ciha]

Unfortunately, the back button on the keyboard isn't obvious on Command Palette Version 0.2.1.0 (PowerToys v0.91.1), which could be an accessibility issue. I tried using enter, space, esc, and backspace when the back arrow button has focus.

[jiripolasek]

Implemented in #40517