Add pathListSeparator predefined variable with : alias

[Copilot]

Adds ${pathListSeparator} (alias ${:}) predefined variable that resolves to the OS-specific path list separator: ; on Windows, : on POSIX. Enables cross-platform configuration of environment variables like PATH, PYTHONPATH, and CLASSPATH.

Changes

• Variable definition: Added PathListSeparator and PathListSeparatorAlias to VariableKind enum
• Resolution logic: Returns paths.delimiter for both ${pathListSeparator} and ${:}
• Autocomplete: Added to configuration-editing extension for launch.json, tasks.json, and .code-workspace files
• Tests: Added platform-specific tests verifying correct separator resolution

Usage

// tasks.json
{
  "env": {
    "PATH": "${workspaceFolder}/bin${pathListSeparator}${env:PATH}",
    "PYTHONPATH": "${workspaceFolder}/src${:}${workspaceFolder}/lib"
  }
}

Follows the same pattern as existing ${pathSeparator} (alias ${/}) for file path separators.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feature Request] Add predefined variable with separator for environment variable PATH (also PYTHONPATH, CLASSPATH etc.)</issue_title>
<issue_description>

I would like to request a new predefined variable, e.g. ${pathListSeparator}, that would be substituted with the separator used in the operating system's PATH environment variable, e.g. : for POSIX or ; for Windows.

Similarly to this feature request regarding ${pathSeparator}, I would also like it to have a shorter alias for improved readability, e.g. ${:}.

The variable could be used for modifications of not only the OS's PATH but also other environment variables that follow the same convention, e.g. Python's PYTHONPATH, Java's CLASSPATH, etc.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature Request] Add predefined variable with separator for environment variable PATH (also PYTHONPATH, CLASSPATH etc.) #180830

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