New givens syntax does no logger accepts valid given defintions

[WojciechMazur]

Based on OpenCB failure in jphmrst/scala-automata - build logs
Affects also:

• rssh/cps-async-connect - build logs

The new givens syntax and its changes to the parser no longer accept valid old (pre 3.6.0) givens syntax, in cases when type of the type-class is moved to the next line. It's a common issue that might be introduced by automatic code formatters when dealing with long names or signatures of given.

Compiler version

Last good release: 3.6.0-RC1-bin-20241003-a672e05-NIGHTLY
First bad release: 3.6.0-RC1-bin-20241005-6fa81cf-NIGHTLY

Bisect points to: 14acdc0

Minimized code

trait Typeclass[T]:
  def op(v: T): Unit

given namedGivenWithLongName[T]:
  Typeclass[T] with
    override def op(v: T): Unit = ???

given otherNamedGivenWithLongName[T]:
  Typeclass[T] = new Typeclass[T]:
    override def op(v: T): Unit = ???

Output

[error] ./test2.scala:5:16
[error] end of statement expected but 'with' found
[error]   Typeclass[T] with
[error]                ^^^^
[error] ./test2.scala:4:7
[error] Not found: type namedGivenWithLongName
[error] given namedGivenWithLongName[T]:
[error]       ^^^^^^^^^^^^^^^^^^^^^^
[error] ./test2.scala:4:30
[error] Not found: type T
[error] given namedGivenWithLongName[T]:
[error]                              ^
[error] ./test2.scala:5:13
[error] Not found: type T
[error]   Typeclass[T] with
[error]             ^
[error] ./test2.scala:5:3
[error] Not found: Typeclass
[error]   Typeclass[T] with
[error]   ^^^^^^^^^

Workaround

Compile with -source:3.5

Expectation

It should compile and be parsable until deprecating the old syntax.

[Gedochao]

cc @odersky