Retain position of extension function calls

[Kordyjan]

Fixes #11523.

[bishabosha]

Thanks for taking this on!

I tried with right associative operator extension applications, which still have a zero length span, e.g.

package ext

extension (s: String)
  def :*: (i: Int): (String, Int) = (s, i)

val b = "foo" :*: 23

yields

expect/Extension.scala
----------------------

Summary:
Schema => SemanticDB v4
Uri => Extension.scala
Text => empty
Language => Scala
Symbols => 5 entries
Occurrences => 14 entries

Symbols:
ext/Extension$package. => final package object ext
ext/Extension$package.`:*:`(). => method :*:
ext/Extension$package.`:*:`().(i) => param i
ext/Extension$package.`:*:`().(s) => param s
ext/Extension$package.b. => val method b

Occurrences:
[0:8..0:11): ext <- ext/
[2:0..2:0): <- ext/Extension$package.
[2:11..2:12): s <- ext/Extension$package.`:*:`().(s)
[2:14..2:20): String -> scala/Predef.String#
[3:6..3:9): :*: <- ext/Extension$package.`:*:`().
[3:11..3:12): i <- ext/Extension$package.`:*:`().(i)
[3:14..3:17): Int -> scala/Int#
[3:21..3:27): String -> scala/Predef.String#
[3:29..3:32): Int -> scala/Int#
[3:37..3:37): -> scala/Tuple2.apply().
[3:37..3:38): s -> ext/Extension$package.`:*:`().(s)
[3:40..3:41): i -> ext/Extension$package.`:*:`().(i)
[5:4..5:5): b <- ext/Extension$package.b.
[5:14..5:14): -> ext/Extension$package.`:*:`(). // Note: zero length span here

we should probably watch out for possible interaction with the selectSpan method: https://github.com/lampepfl/dotty/blob/4ed026cb7c0e3e1f97456172e382f199c1aea8da/compiler/src/dotty/tools/dotc/semanticdb/ExtractSemanticDB.scala#L515

[Kordyjan]

I solved the problem with inline operators by adding an attachment containing the original span of the operator. I don't think there is any nicer way of passing this information for synthesized selects.

[bishabosha]

LGTM, I have found an optimisation without attachments

[bishabosha]

I tried this which did not need any attachments (I don't think its that important to do the point span for synthetic):

def nameSpan(using Context): Span =
  if span.exists then
    val point = span.point
    if name.toTermName == nme.ERROR then Span(point)
    else if qualifier.span.start > span.start then // right associative
      val realName = name.stripModuleClassSuffix.lastPart
      Span(span.start, span.start + realName.length, point)
    else
      Span(point, span.end, point)
  else span