Add top-level definitions to scope in TreeMapWithImplicits

[nicolasstucki]

Fixes #11479

[nicolasstucki]

Reproduce current issues with

sbt> testCompilation tests/pos/t3642

or

sbt> testCompilation --from-tasty <test-name>
// were <test-name> is one of
// tests/run/inlineAddDeserializeLambda.scala
// tests/run/inline-param-semantics.scala
// tests/run/rescue.scala
// tests/run/erased-inline-vals.scala
// tests/run/tuple-ops.scala
// tests/run/toList.scala
// tests/run/enum-nat.scala
// tests/run/transparent-object.scala
// tests/run/i8530.scala
// tests/run/inline-override.scala
// tests/run/i8058.scala
// tests/run/i4496b.scala
// tests/run/tuples-empty.scala
// tests/run/i9473.scala
// tests/run/constValueTuple.scala
// tests/run/i10724.scala
// tests/run/i7110.scala
// tests/run/singleton-ops-flags.scala
// tests/run/i8530-b.scala
// tests/run/tuple-product.scala
// tests/run/typelevel-overrides.scala
// tests/run/transparent-foreach.scala
// tests/run/reduce-projections.scala
// tests/run/transparentProtected.scala
// tests/run/summonAll.scala
// tests/run/fragables-extension.scala
// tests/run/inline-override-num.scala
// tests/run/i2360.scala
// tests/run/i4523.scala
// tests/run/dead-code-elimination.scala
// tests/run/typeCheckErrors.scala
// tests/run/implicit-functors2.scala
// tests/pos/t3642

[nicolasstucki]

Replaced by #11591