Do not lint multiarg for mixed op def

[som-snytt]

Follow-up per review by @SethTisue

Remove lint of definition of lines_!, which is arguably innocent.

[SethTisue]

context is #8951 (comment)

[SethTisue]

couldn't isOperatorName just be defined as isOperatorChar(decoded.head)? (he asked innocently, bracing himself for a lesson on why we can't have nice things)

[som-snytt]

Actually, Seth, after I boned up (so to speak) on NameTransformer, I was too tired to overthink it. The comment was that the IDE used it. A name can be arbitrarily junk. Like boldface.

scala> TermName("x")
val res0: u.TermName = x

scala> TermName("*x*")
val res1: u.TermName = *x*

[som-snytt]

As usual, I wound up taking Seth's advice. isOperatorName is used in a couple of places (reflection uses it to decide whether to print backquoted idents). A test actually tests a*.

Since we only care about legal idents, the lint only checks for leading op char.

Oh wait, there's still the question of backticks. Oh wait, I'm too tired.

[SethTisue]

LGTM, and this still seems right to me even if backticks enter the picture. But perhaps one more reviewer would like to ponder all of this at least a little before we hit "merge".

[eed3si9n]

@SethTisue

couldn't isOperatorName just be defined as isOperatorChar(decoded.head)? (he asked innocently, bracing himself for a lesson on why we can't have nice things)

Here's a counter example: def unary_! : Foo = this

There's a whitespace between ! and : required, and name.isOperatorName is used to check for that kind of stuff in Printers

scala/src/reflect/scala/reflect/internal/Printers.scala

Lines 597 to 598 in 8aefe5e

	protected def blankForOperatorName(name: Name) = checkForBlank(name.isOperatorName)
	protected def blankForName(name: Name) = checkForBlank(name.isOperatorName || name.endsWith("_"))