[lldb] Reduce max-children-count default to readable size

Change the default from 256 to 24. The argument is that 256 is too large to be scanned
by eye, and too large to print in a terminal which can be only 40-50 lines in height.

When all children must be shown, `frame variable` and `expression` both support the `-A`
(`--show-all-children`) flag.

rdar://145327522

Author: kastiglione

lldb/source/Target/TargetProperties.td

@@ -96,7 +96,7 @@ let Definition = "target" in {
     DefaultUnsignedValue<6>,
     Desc<"The maximum number of zeroes to insert when displaying a very small float before falling back to scientific notation.">;
   def MaxChildrenCount: Property<"max-children-count", "UInt64">,
-    DefaultUnsignedValue<256>,
+    DefaultUnsignedValue<24>,
     Desc<"Maximum number of children to expand in any level of depth.">;
   def MaxChildrenDepth: Property<"max-children-depth", "UInt64">,
     DefaultUnsignedValue<0xFFFFFFFF>,

lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/forward_list/TestDataFormatterGenericForwardList.py

@@ -50,7 +50,7 @@ def do_test(self, stdlib_type):
         self.expect(
             "settings show target.max-children-count",
             matching=True,
-            substrs=["target.max-children-count (unsigned) = 256"],
+            substrs=["target.max-children-count (unsigned) = 24"],
         )
 
         self.expect(

lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/list/TestDataFormatterGenericList.py

@@ -50,7 +50,6 @@ def cleanup():
             self.runCmd("type summary clear", check=False)
             self.runCmd("type filter clear", check=False)
             self.runCmd("type synth clear", check=False)
-            self.runCmd("settings set target.max-children-count 256", check=False)
 
         # Execute the cleanup function during test case tear down.
         self.addTearDownHook(cleanup)

lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/multimap/TestDataFormatterGenericMultiMap.py

@@ -65,7 +65,6 @@ def cleanup():
             self.runCmd("type summary clear", check=False)
             self.runCmd("type filter clear", check=False)
             self.runCmd("type synth clear", check=False)
-            self.runCmd("settings set target.max-children-count 256", check=False)
 
         # Execute the cleanup function during test case tear down.
         self.addTearDownHook(cleanup)

lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/multiset/TestDataFormatterGenericMultiSet.py

@@ -51,7 +51,6 @@ def cleanup():
             self.runCmd("type summary clear", check=False)
             self.runCmd("type filter clear", check=False)
             self.runCmd("type synth clear", check=False)
-            self.runCmd("settings set target.max-children-count 256", check=False)
 
         # Execute the cleanup function during test case tear down.
         self.addTearDownHook(cleanup)

lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/set/TestDataFormatterGenericSet.py

@@ -51,7 +51,6 @@ def cleanup():
             self.runCmd("type summary clear", check=False)
             self.runCmd("type filter clear", check=False)
             self.runCmd("type synth clear", check=False)
-            self.runCmd("settings set target.max-children-count 256", check=False)
 
         # Execute the cleanup function during test case tear down.
         self.addTearDownHook(cleanup)

lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic/unordered/TestDataFormatterGenericUnordered.py

@@ -33,7 +33,6 @@ def cleanup():
             self.runCmd("type summary clear", check=False)
             self.runCmd("type filter clear", check=False)
             self.runCmd("type synth clear", check=False)
-            self.runCmd("settings set target.max-children-count 256", check=False)
             self.runCmd("settings set auto-one-line-summaries true", check=False)
 
         # Execute the cleanup function during test case tear down.

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/TestDataFormatterLibccIterator.py

@@ -43,7 +43,6 @@ def cleanup():
             self.runCmd("type summary clear", check=False)
             self.runCmd("type filter clear", check=False)
             self.runCmd("type synth clear", check=False)
-            self.runCmd("settings set target.max-children-count 256", check=False)
 
         # Execute the cleanup function during test case tear down.
         self.addTearDownHook(cleanup)

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/map/TestDataFormatterLibccMap.py

@@ -50,7 +50,6 @@ def cleanup():
             self.runCmd("type summary clear", check=False)
             self.runCmd("type filter clear", check=False)
             self.runCmd("type synth clear", check=False)
-            self.runCmd("settings set target.max-children-count 256", check=False)
 
         # Execute the cleanup function during test case tear down.
         self.addTearDownHook(cleanup)

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string/TestDataFormatterLibcxxString.py

@@ -41,7 +41,6 @@ def cleanup():
             self.runCmd("type summary clear", check=False)
             self.runCmd("type filter clear", check=False)
             self.runCmd("type synth clear", check=False)
-            self.runCmd("settings set target.max-children-count 256", check=False)
 
         is_64_bit = self.process().GetAddressByteSize() == 8