Source sweep: Use cmStrCat for string concatenation

This patch is generated by a python script that uses regular expressions to
search for string concatenation patterns of the kind

```
std::string str = <ARG0>;
str += <ARG1>;
str += <ARG2>;
...
```

and replaces them with a single `cmStrCat` call

```
std::string str = cmStrCat(<ARG0>, <ARG1>, <ARG2>, ...);
```

If any `<ARGX>` is itself a concatenated string of the kind

```
a + b + c + ...;
```

then `<ARGX>` is split into multiple arguments for the `cmStrCat` call.

If there's a sequence of literals in the `<ARGX>`, then all literals in the
sequence are concatenated and merged into a single literal argument for
the `cmStrCat` call.

Single character strings are converted to single char arguments for
the `cmStrCat` call.

`std::to_string(...)` wrappings are removed from `cmStrCat` arguments,
because it supports numeric types as well as string types.

`arg.substr(x)` arguments to `cmStrCat` are replaced with
`cm::string_view(arg).substr(x)`

Source/cmScriptGenerator.cxx

@@ -2,6 +2,7 @@
    file Copyright.txt or https://cmake.org/licensing for details.  */
 #include "cmScriptGenerator.h"
 
+#include "cmStringAlgorithms.h"
 #include "cmSystemTools.h"
 
 #include <utility>
@@ -51,9 +52,8 @@ static void cmScriptGeneratorEncodeConfig(const std::string& config,
 
 std::string cmScriptGenerator::CreateConfigTest(const std::string& config)
 {
-  std::string result = "\"${";
-  result += this->RuntimeConfigVariable;
-  result += "}\" MATCHES \"^(";
+  std::string result =
+    cmStrCat("\"${", this->RuntimeConfigVariable, "}\" MATCHES \"^(");
   if (!config.empty()) {
     cmScriptGeneratorEncodeConfig(config, result);
   }
@@ -64,9 +64,8 @@ std::string cmScriptGenerator::CreateConfigTest(const std::string& config)
 std::string cmScriptGenerator::CreateConfigTest(
   std::vector<std::string> const& configs)
 {
-  std::string result = "\"${";
-  result += this->RuntimeConfigVariable;
-  result += "}\" MATCHES \"^(";
+  std::string result =
+    cmStrCat("\"${", this->RuntimeConfigVariable, "}\" MATCHES \"^(");
   const char* sep = "";
   for (std::string const& config : configs) {
     result += sep;