Avoid shadowing of name 'name'

[som-snytt]

Fixes #13440

[som-snytt]

Reopen for rebase.

[som-snytt]

As a refresher, HEAD says

-- [E040] Syntax Error: /tmp/i13440.scala:6:11 --------------------------------------------------------------------------------------------------
6 |  val s = s"$enum" // error
  |           ^
  |           '}' expected, but string literal found
-- Error: /tmp/i13440.scala:6:17 ----------------------------------------------------------------------------------------------------------------
6 |  val s = s"$enum" // error
  |                 ^
  |                 unclosed string literal
exception occurred while parser /tmp/i13440.scala
exception occurred while compiling /tmp/i13440.scala
java.lang.NullPointerException: Cannot invoke "dotty.tools.dotc.core.Names$SimpleName.length()" because the return value of "dotty.tools.dotc.parsing.Scanners$Scanner.name()" is null while compiling /tmp/i13440.scala
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "dotty.tools.dotc.core.Names$SimpleName.length()" because the return value of "dotty.tools.dotc.parsing.Scanners$Scanner.name()" is null
        at dotty.tools.dotc.parsing.Scanners$Scanner.treatAsIdent(Scanners.scala:255)
        at dotty.tools.dotc.parsing.Scanners$Scanner.handleMigration(Scanners.scala:246)
        at dotty.tools.dotc.parsing.Scanners$Scanner.toToken(Scanners.scala:260)
        at dotty.tools.dotc.parsing.Scanners$ScannerCommon.finishNamed(Scanners.scala:146)
        at dotty.tools.dotc.parsing.Scanners$Scanner.getStringPart(Scanners.scala:1171)
        at dotty.tools.dotc.parsing.Scanners$Scanner.stringPart$1(Scanners.scala:786)
        at dotty.tools.dotc.parsing.Scanners$Scanner.fetchDoubleQuote$1(Scanners.scala:807)
        at dotty.tools.dotc.parsing.Scanners$Scanner.fetchToken(Scanners.scala:826)
        at dotty.tools.dotc.parsing.Scanners$Scanner.nextToken(Scanners.scala:343)
        at dotty.tools.dotc.parsing.Parsers$Parser.interpolatedString(Parsers.scala:1192)

[odersky]

Hi Tim, could you take a look at this? Thanks?

[som-snytt]

@griggt Thanks, Tom?