Web: dialog button default is wrong

[bpasero]

Steps to Reproduce:

1. macOS undo some changes from SCM view
2. with native, I can just press enter, in web the default seems to be "Cancel"

[bpasero]

PR: #77266

@sbatten I suggest you take a look how we handle dialogs in electron for specific platforms: massageMessageBoxOptions

There are possibly more things to consider.

[sbatten]

@bpasero From what I see in that method, there is just button reversal on non-windows and special placement of the cancel button which seems the same as the logic @lramos15 added in rearrangeButtons