Uplift #1805 to 0.63 - OS appearance mode controls Brave appearance mode (light / dark theme)

[petemill]

This is an uplift request for 0.63.x of #1805.
Reason for uplift request is that C63 has the 'Same as macOS' theme functionality launched in chrome. That is, the chrome light / dark mode will follow the macOS light / dark appearance mode. Without this PR, Brave will not automatically change, and has to be done manually from Settings.

Therefore this can be seen as a regression fix for 2 reasons:

1. There is a mismatch between some Brave controls when choosing a theme that is different to the user's OS theme. I.e. the toolbar can be in a light theme whilst the info popups and menus would be in a dark theme.

Like this:

2. Upstream supports changing light / dark mode based on OS but Brave breaks this functionality.

Fix brave/brave-browser#1189
Fix brave/brave-browser#1289

[kjozwiak]

Uplift to 0.63.x approved after deliberating with @srirambv & @bbondy. Please make sure that all associated issues are moved into the correct milestones.

@petemill before merging, can you double check the Jenkins failure and make sure there's no issues?

[simonhong]

After merging this, we should uplift #1958 also.
This PR will cause compile error on buildbot.
I'll check two PR on beta/dev branch on my local first.

[kjozwiak]

After merging this, we should uplift #1958 also.
This PR will cause compile error on buildbot.
I'll check two PR on beta/dev branch on my local first.

Thanks @simonhong, let me know if we end up needing #1958 as well.

[simonhong]

@kjozwiak This PR was fine on my local but want to double check about the log from This commit cannot be built. Can you paste that log here? I think I need to request to access permission soon :)