Fix partest compilation of java-interop tests by moving them

Previously, the tests where all in tests/pos/java-interop which means
that partest would try to run them as one single test, this failed
because some of these tests define classes with the same name. We could
fix this by putting them all in separate packages but for now it's
simple to move them to tests/pos-java-interop (they will still be run
individually as they should thanks to the `java_all` test defined in
tests.scala)

Author: smarter

test/dotc/tests.scala

@@ -249,7 +249,7 @@ class tests extends CompilerTest {
       dotcDir + "config/PathResolver.scala"
     ), List(/* "-Ylog:frontend", */ "-Xprompt") ++ staleSymbolError ++ twice)
 
-  val javaDir = "./tests/pos/java-interop/"
+  val javaDir = "./tests/pos-java-interop/"
   @Test def java_all = compileFiles(javaDir, twice)
   //@Test def dotc_compilercommand = compileFile(dotcDir + "config/", "CompilerCommand")