[Feature] Support for toolset version v141_xp

### Request Overview

The toolset version value v141_xp is not supported:

```
{
"version": 6,
"configurePresets": [
{
"name": "windows-x86-Release",
"generator": "Ninja",
"binaryDir": "${sourceDir}/cmake-build-${presetName}",
"cacheVariables": {
"CMAKE_C_COMPILER": "cl.exe",
"CMAKE_CXX_COMPILER": "cl.exe",
"CMAKE_EXPORT_COMPILE_COMMANDS": "ON",
"CMAKE_BUILD_TYPE": "Release"
},
"architecture": {
"value": "x86",
"strategy": "external"
},
"toolset": {
"value": "v141_xp,host=x86",
"strategy": "external"
}
}
]
}
```

### Additional Information

_No response_

No source file or test is named. Start by locating the configure-preset toolset validation and existing tests for supported toolset values; the work is done when a preset using v141_xp, including the shown host=x86 form, is accepted and covered by a test.

Written by the indexing model from the issue text.