Add tests for context bounds migration (#19510)

Improves tests of #19316

tests/neg/context-bounds-migration-3.5.check

@@ -0,0 +1,6 @@
+-- Error: tests/neg/context-bounds-migration-3.5.scala:9:2 -------------------------------------------------------------
+9 |  foo(C[Int]()) // error
+  |  ^^^
+  |  Context bounds will map to context parameters.
+  |  A `using` clause is needed to pass explicit arguments to them.
+  |  This code can be rewritten automatically under -rewrite -source 3.4-migration.

tests/neg/context-bounds-migration-3.5.scala

@@ -0,0 +1,10 @@
+//> using options -source 3.5
+
+class C[T]
+def foo[X: C] = ()
+
+given [T]: C[T] = C[T]()
+
+def Test =
+  foo(C[Int]()) // error
+  foo(using C[Int]()) // ok

tests/neg/context-bounds-migration-future.check

@@ -0,0 +1,6 @@
+-- [E050] Type Error: tests/neg/context-bounds-migration-future.scala:9:2 ----------------------------------------------
+9 |  foo(C[Int]()) // error
+  |  ^^^
+  |  method foo does not take more parameters
+  |
+  | longer explanation available when compiling with `-explain`

tests/neg/context-bounds-migration-future.scala

@@ -0,0 +1,10 @@
+//> using options -source future
+
+class C[T]
+def foo[X: C] = ()
+
+given [T]: C[T] = C[T]()
+
+def Test =
+  foo(C[Int]()) // error
+  foo(using C[Int]()) // ok

tests/warn/context-bounds-migration-3.4.check

@@ -0,0 +1,6 @@
+-- Warning: tests/warn/context-bounds-migration-3.4.scala:9:2 ----------------------------------------------------------
+9 |  foo(C[Int]())  // warn
+  |  ^^^
+  |  Context bounds will map to context parameters.
+  |  A `using` clause is needed to pass explicit arguments to them.
+  |  This code can be rewritten automatically under -rewrite -source 3.4-migration.