Setting min-width for buttons (l10n-friendly)

[luixxiul]

Did you search for similar issues before submitting this one?

Describe the issue you encountered:
From a perspective of localization the min-width of the buttons should be specified to avoid the case like this:

Expected behavior:
CC @bradleyrichter for thought

• Brave Version (revision SHA): f27bb94

• Any related issues: Refactor buttons on about:preferences#payments and bookmark dialog #5705 Button tweak prefs font nicer #6000 (comment)

These are almost all of the buttons that should be considered (courtesy of @srirambv) #6372

Please exclude the buttons on the Add funds dialog.

0.13.0 vs 0.12.15

[bradleyrichter]

I think it is perfectly logical to set a min width for buttons.

6 characters plus padding is a good measurement:

[luixxiul]

Test Plan:

1. Open about:autofill
2. Click "Add Address"
3. Make sure the width of the button "Cancel" and "Save" is equal