cmSystemTools: Add ExpandedListArgument and ExpandedLists methods

Changes
-------

In `cmSystemTools` this
- renames the method `ExpandList` to `ExpandLists` and makes it iterator based

and adds the methods
- `std::vector<std::string> ExpandedLists(InputIt first, InputIt last)`
- `std::vector<std::string> ExpandedListArgument(const std::string& arg,
                                                       bool emptyArgs)`

Both return the  `std::vector<std::string>` instead of taking a return vector
reference like `cmSystemTools::ExpandLists` and
`cmSystemTools::ExpandListArgument`.

Motivation
----------

Since C++17 return value optimization is mandatory, so returning a
`std:vector<std::string>` from a function should be (at least) as fast as
passing a return vector reference to the function.

The new methods can replace `cmSystemTools::ExpandLists` and
`cmSystemTools::ExpandListArgument` in many cases, which leads to
shorter and simpler syntax.

E.g. the commonly used pattern
```
  if (const char* value = X->GetProperty("A_KEY_STRING")) {
    std::vector<std::string> valuesList;
    cmSystemTools::ExpandListArgument(value, valuesList);
    for (std::string const& i : valuesList) {
      doSomething(i);
    }
  }
```
becomes
```
  if (const char* value = X->GetProperty("A_KEY_STRING")) {
    for (std::string const& i :
      cmSystemTools::ExpandedListArgument(value)) {
      doSomething(i);
    }
  }
```

1 files changed, 4 insertions, 6 deletions

diff --git a/Source/cmGlobalXCodeGenerator.cxx b/Source/cmGlobalXCodeGenerator.cxx
index db673bb..6cbdefa 100644
--- a/Source/cmGlobalXCodeGenerator.cxx
+++ b/Source/cmGlobalXCodeGenerator.cxx
@@ -2485,12 +2485,10 @@ cmXCodeObject* cmGlobalXCodeGenerator::CreateUtilityTarget(
 std::string cmGlobalXCodeGenerator::AddConfigurations(cmXCodeObject* target,
                                                       cmGeneratorTarget* gtgt)
 {
-  std::string configTypes =
-    this->CurrentMakefile->GetRequiredDefinition("CMAKE_CONFIGURATION_TYPES");
-  std::vector<std::string> configVectorIn;
-  std::vector<std::string> configVector;
-  configVectorIn.push_back(configTypes);
-  cmSystemTools::ExpandList(configVectorIn, configVector);
+  std::vector<std::string> const configVector =
+    cmSystemTools::ExpandedListArgument(
+      this->CurrentMakefile->GetRequiredDefinition(
+        "CMAKE_CONFIGURATION_TYPES"));
   cmXCodeObject* configlist =
     this->CreateObject(cmXCodeObject::XCConfigurationList);
   cmXCodeObject* buildConfigurations =