Native: add debugger test for inspecting string variables

We just had no tests checking that debugger can properly show values
of string-typed variables. This commit adds such a test.

native/native.tests/testData/lldb/canInspectStrings.kt

@@ -0,0 +1,10 @@
+// KIND: STANDALONE_LLDB
+// LLDB_TRACE: canInspectStrings.txt
+fun main(args: Array<String>) {
+    val a = "string literal"
+    val b = buildString {
+        append("dynamic ")
+        append("string")
+    }
+    return
+}

native/native.tests/testData/lldb/canInspectStrings.txt

@@ -0,0 +1,6 @@
+> b main.kt:9
+> r
+> fr var
+(ObjHeader *) a = string literal
+(ObjHeader *) b = dynamic string
+> q