Require Site Isolation for every site

Since Brave 67, site isolation has been enabled by default on all Desktop platforms, causing every site to run in its own process. A site is a scheme plus eTLD+1 (e.g., https://example.com). Setting this policy to Enabled does not change that behavior; it only prevents users from opting out (for example, using Disable site isolation in chrome://flags). Since Brave 76, setting the policy to Disabled or leaving it unset doesn't turn off site isolation, but instead allows users to opt out. IsolateOrigins might also be useful for isolating specific origins at a finer granularity than site (e.g., https://a.example.com). On Google Chrome OS version 76 and earlier, set the DeviceLoginScreenSitePerProcess device policy to the same value. (If the values don't match, a delay can occur when entering a user session.) Note: For Android, use the SitePerProcessAndroid policy instead.