[Feature request] Make `executorMap` behave differently for different OS platforms

It would solve many problems if the extension could identify the operating
system platform and run different executors.

Description of what would be a minimal interface:

```json
{
"code-runner.executorMap.windows": {
"python": "python",
"html": "\"C:\\Program Files (x86)\\Google\\Chrome\\Application\\chrome.exe\"",
"c": "cd $dir && cl.exe $fileName -o $fileNameWithoutExt && $dir$fileNameWithoutExt"
},
"code-runner.executorMap.linux": {
"python": "python3",
"html": "/usr/local/bin/chrome",
"c": "cd $dir && gcc $fileName -o $fileNameWithoutExt && $dir$fileNameWithoutExt"
}
}
```

Related issues (still open)
- #350
- #1049

Start by locating the executorMap configuration handling and the extension entry point, then trace how executor commands are selected. Define platform-specific settings for the Windows and Linux examples, and verify that the appropriate Python, HTML, and C executors are selected without changing existing behavior.

Written by the indexing model from the issue text.