User permission fixes

[islemaster]

Some updates to the UserPermissionGrantee implementation suggested by @aoby while reviewing #23329.

• revoke_all_permissions should clear the user's permissions cache.
• Dynamically define user permission helper methods like levelbuilder?

[aoby]

What is the point of this call? We don't check the return

[islemaster]

This first call to permission? populates the permission cache, so we can later check that it's cleared.

I lifted this approach from the caching test that I copied over:

code-dot-org/dashboard/test/models/user_test.rb

Lines 1938 to 1946 in 279f685

	test 'permission? caches all permissions' do
	user = create :facilitator
	user.permission?(UserPermission::LEVELBUILDER)
	no_database
	assert user.permission?(UserPermission::FACILITATOR)
	refute user.permission?(UserPermission::LEVELBUILDER)
	end

I didn't come up with a way to assert that the cache has been filled without the no_database call the previous test uses. Maybe, in turn, this needs a comment?

[aoby]

That makes sense. I'd either add a comment, or instead override reload_permissions to also refresh that @permissions cache and call that.