Browser's external editor von Ruslan Osmanov

New Feature: Support for ${line} and ${column} placeholders in the command line settings

The Command Line field in the extension settings now supports two new placeholders:
- ${line} for the 1-based line number
- ${column} for the 1-based column number (offset from the beginning of the line)

Example usage:
/usr/local/bin/gvim --nofork +"call cursor(${line}, ${column})"

Notes:
- Quotes (single or double) are expanded similarly to shells.
- Variable expansion (like $VAR) and backslash escaping are not supported.
- Quotes are required when passing arguments that contain spaces. Without quotes, a line like +call cursor(${line}, ${column}) would be split into three arguments: +call, cursor(${line}, and ${column}).