Move blackBoxFile() testData to box/ directory

Delete all test methods (and empty test classes), since they'll be
auto-generated

compiler/testData/codegen/box/strings/multilineStringsWithTemplates.kt

@@ -0,0 +1,31 @@
+fun box() : String {
+    val s = "abc"
+    val test1 = """$s"""
+    if (test1 != "abc") return "Fail 1: $test1"
+
+    val test2 = """${s}"""
+    if (test2 != "abc") return "Fail 2: $test2"
+
+    val test3 = """ "$s" """
+    if (test3 != " \"abc\" ") return "Fail 3: $test3"
+
+    val test4 = """ "${s}" """
+    if (test4 != " \"abc\" ") return "Fail 4: $test4"
+
+    val test5 =
+"""
+  ${s.length}
+"""
+    if (test5 != "\n  3\n") return "Fail 5: $test5"
+
+    val test6 = """\n"""
+    if (test6 != "\\n") return "Fail 6: $test6"
+
+    val test7 = """\${'$'}foo"""
+    if (test7 != "\\\$foo") return "Fail 7: $test7"
+
+    val test8 = """$ foo"""
+    if (test8 != "$ foo") return "Fail 8: $test8"
+
+    return "OK"
+}