Add scripted test for excludeFilter

It was reported in #4868 that exclueFilters didn't work correctly if
there was an || in the filter. This was an upstream issue in io, but
this commit adds a scripted test in sbt.

sbt/src/sbt-test/nio/legacy-filters/build.sbt

@@ -0,0 +1,8 @@
+Compile / excludeFilter := "Bar.scala" || "Baz.scala"
+
+val checkSources = inputKey[Unit]("Check that the compile sources match the input file names")
+checkSources := {
+  val sources = Def.spaceDelimited("").parsed.toSet
+  val actual = (Compile / unmanagedSources).value.map(_.getName).toSet
+  assert(sources == actual)
+}

sbt/src/sbt-test/nio/legacy-filters/src/main/scala/Bar.scala

@@ -0,0 +1 @@
+class Bar {

sbt/src/sbt-test/nio/legacy-filters/src/main/scala/Foo.scala

@@ -0,0 +1 @@
+class Foo

sbt/src/sbt-test/nio/legacy-filters/test

@@ -0,0 +1,9 @@
+> checkSources Foo.scala
+
+> compile
+
+> set Compile / excludeFilter := HiddenFileFilter
+
+> checkSources Foo.scala Bar.scala
+
+-> compile