[Android] Add support for #enable-force-dark

[anthonypkeane]

Description

See: https://bravesoftware.slack.com/archives/C0816QH3R/p1596571834338300

Enable support for #enable-force-dark

Add a setting in Settings > Display > Appearance
As the top menu item add

Enable "Night Mode"

Exact label text TBD

[srirambv]

Enable "Night Mode" should be Enable "Night Mode" (Experimental)

[srirambv]

Verification passed on OnePlus 6T with Android 10 running 1.15.54 x64 beta build

• Verified new settings option Enable "Night Mode"(Experimental) is listed under Settings -> Appearance
• Verified enabling/disabling the settings prompts for a relaunch
• Veriifed selecting later in relaunch prompt doesn't cause the webview to either go dark or remain white until browser is restarted
• Verified enabling the settings enables the flag chrome://flags#enable-force-dark
• Verified enabling the settings causes webview to be dark mode

Setting	Restart alert	Flag	Dark webview

Logged followup issue for missing translation #11781

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Tablet test blocked on #11783

Verification passed on Samsung Tab A with Android 10 running 1.15.54 x64 beta build

• Verified new settings option Enable "Night Mode"(Experimental) is listed under Settings -> Appearance
• Verified enabling/disabling the settings prompts for a relaunch
• Verified selecting later in relaunch prompt doesn't cause the webview to either go dark or remain white until the browser is restarted
• Verified enabling the settings enables the flag chrome://flags#enable-force-dark
• Verified enabling the settings causes webview to be dark mode

Setting	Restart alert	Flag	Dark webview

[Dev-i-l]

PLEASE MAKE SURE THAT DARK MODE IS ACCESSIBLE THROUGH 3-DOT MENU.