Add tests for enhanced java signatures based on AbstractResolvedCallsTest.

Refactor AbstractResolvedCallsTest to support multiple carets (multiple methods being tested  for resolve) in testdata file.

compiler/testData/resolvedCalls/enhancedSignatures/optional/optionalEmpty.txt

@@ -0,0 +1,13 @@
+import java.util.*
+
+fun use() {
+    Optional.empty<String>()
+        // SUCCESS
+        // ORIGINAL:    fun <T : Any!> empty(): Optional<T> defined in java.util.Optional
+        // SUBSTITUTED: fun <T : Any!> empty(): Optional<String> defined in java.util.Optional
+    Optional.empty<String?>()
+        // SUCCESS
+        // ORIGINAL:    fun <T : Any!> empty(): Optional<T> defined in java.util.Optional
+        // SUBSTITUTED: fun <T : Any!> empty(): Optional<String> defined in java.util.Optional
+}
+