Disable components by default sourced from block plugins provided by core in the Standard profile

In a Slack conversation between Wim and I, Wim suggested that we do this in code rather than config, and that "programmatic would be safer, unless you add a test that fails if the set of expected core block plugins change", then added: "[Tests are] necessary anyway. Because we want our decisions to cover all core block plugins always."

Given that this is a temporary solution, I don't think we need to put a lot of emphasis on the correctness, but I'll leave that to Wim to decide. One thing I would add is that we do want users to be able to enable these blocks (components representing block plugins) if they decide to do so.