[lldb][test] Add tests for target.max-string-summary-length setting (#77920)

This adds API tests for the `target.max-string-summary-length`, which
was recently fixed in #72233

Author: Michael137

lldb/test/API/functionalities/data-formatter/data-formatter-advanced/TestDataFormatterAdv.py

@@ -295,6 +295,23 @@ def cleanup():
             substrs=["e_2", "n_2", "r_2", "i_2", "k_2", "o_2"],
         )
 
+        self.runCmd("settings set target.max-string-summary-length 5")
+        some_string = self.frame().FindVariable("some_string")
+        some_string_summary = some_string.GetSummary()
+        self.assertEqual(some_string_summary, '"01234"...')
+
+        some_carr = self.frame().FindVariable("some_carr")
+        some_carr_summary = some_carr.GetSummary()
+        self.assertEqual(some_carr_summary, '"01234"...')
+
+        # FIXME: c-strings should honor the target.max-string-summary-length
+        # setting. Currently a C-string will be truncated at 64 (an internal
+        # implementation detail) instead of the value specified in the setting.
+        some_cstring = self.frame().FindVariable("some_cstring")
+        some_cstring_summary = some_cstring.GetSummary()
+        self.assertEqual(len(some_cstring_summary), 66)  # 64 + 2 (for quotation marks)
+        self.assertFalse(some_cstring_summary.endswith("..."))
+
         # override the cap
         self.expect(
             "frame variable a_long_guy --show-all-children",

lldb/test/API/functionalities/data-formatter/data-formatter-advanced/main.cpp

@@ -1,6 +1,7 @@
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <stdint.h>
+#include <string>
 
 struct i_am_cool
 {
@@ -164,6 +165,17 @@ int main (int argc, const char * argv[])
     Simple a_simple_object(3,0.14,'E');
 
     VeryLong a_long_guy;
-    
+
+    std::string some_string = "012345678901234567890123456789"
+                              "012345678901234567890123456789"
+                              "012345678901234567890123456789"
+                              "012345678901234567890123456789";
+    char const *some_cstring = some_string.c_str();
+
+    char const some_carr[] = "012345678901234567890123456789"
+                             "012345678901234567890123456789"
+                             "012345678901234567890123456789"
+                             "012345678901234567890123456789";
+
     return 0; // Set break point at this line.
 }