Test electric.el in plainer c-mode without c-electric-{brace,paren}

Test electric.el in plainer c-mode without c-electric-{brace,paren}

If cc-mode ever drops/changes its usage of c-electric-{brace,paren}
test that electric pairing, layout and indentation based on
electric.el keep working.

* test/lisp/electric-tests.el
(electric-layout-int-main-kernel-style)
(electric-layout-int-main-allman-style): Change order of after and
after-stay.
(plainer-c-mode): New test mode.
(electric-modes-in-c-mode-with-self-insert-command): New test.