Better error message for contextual bounds on type aliases

[hamzaremmal]

Compiler version

93af7b8

Minimized example

trait Equatable[T]
type Foo[T: Equatable]

Output Error/Warning message

-- [E040] Syntax Error: test.scala:3:10 ----------------------------------------
3 |type Foo[T: Equatable]
  |          ^
  |          ']' expected, but ':' found
1 error found

Why this Error/Warning was not helpful

An error message mentioning that context bounds are not allowed is much useful.

Suggested improvement

See above

[mbovel]

This issue was picked for the Scala Issue Spree of today, May 19th. @hamzaremmal, @ajafri2001 and @jan-pieter will be working on it.