Have the asmprinter take advantage of the new capabilities of the asmparser, by

printing the entry block in a CFG function's argument line.  Since I'm touching
all of the testcases anyway, change the argument list from printing as
"%arg : type" to "%arg: type" which is more consistent with bb arguments.

In addition to being more consistent, this is a much nicer look for cfg functions.

PiperOrigin-RevId: 227240069