Add dirSep variable for launch.json

[nrayburn-tech]

Adds a dirSep variable that can be used in launch.json.

Testing

Modify a launch.json config, so that a / is replaced with ${dirSep}. For example, modifying the Gulp Build program property.
From
"${workspaceFolder}/node_modules/gulp/bin/gulp.js" to "${workspaceFolder}${dirName}node_modules${dirName}gulp${dirName}bin${dirName}gulp.js"

This PR fixes #38381

[weinand]

@nrayburn-tech Thanks for the PR.

I suggest to use the name pathSeparator instead of dirSep.
Reasons:

• PathSeparator is the technically correct and more commonly used term.
• we try to avoid abbreviations in variables names (yes, there are exceptions - but for historical reasons...)

Could you please update your PR?

[weinand]

@nrayburn-tech thanks for the PR.
I have renamed your dirSep to the suggest pathSeparator .