[interop][SwiftToCxx] also test for UTF8View API in the test

Author: hyp

test/Interop/SwiftToCxx/stdlib/swift-stdlib-in-cxx.swift

@@ -104,6 +104,18 @@
 // CHECK-NEXT: #endif
 // CHECK-NEXT: private:
 
+// CHECK: class UTF8View final {
+// CHECK:  inline UTF8View(UTF8View &&) { abort(); }
+// CHECK-NEXT: inline String_Index getStartIndex() const;
+// CHECK-NEXT:   inline String_Index getEndIndex() const;
+// CHECK-NEXT:   inline String_Index index(const String_Index& i, swift::Int n) const;
+// CHECK-NEXT:   inline Swift::Optional<String_Index> index(const String_Index& i, swift::Int n, const String_Index& limit) const;
+// CHECK-NEXT:   inline swift::Int distance(const String_Index& i, const String_Index& j) const;
+// CHECK-NEXT: inline uint8_t operator [](const String_Index& i) const;
+// CHECK-NEXT:   inline String getDebugDescription() const;
+// CHECK-NEXT:   inline String getDescription() const;
+// CHECK-NEXT:   inline swift::Int getCount() const;
+
 // CHECK: #if __has_include(<../../../swift/swiftToCxx/_SwiftStdlibCxxOverlay.h>)
 // CHECK-NEXT: #include <../../../swift/swiftToCxx/_SwiftStdlibCxxOverlay.h>
 // CHECK-NEXT: #elif __has_include(<../../../../../lib/swift/swiftToCxx/_SwiftStdlibCxxOverlay.h>)