Add helper for substituting config variables

[koesie10]

This adds a helper for substituting config variables, such as the following:

• .github/codeql/extensions/${name}-${language} becomes .github/codeql/extensions/vscode-codeql-java
• ${owner}/${name}-${language} becomes github/vscode-codeql-java
• ${workspaceFolder}${pathSeparator}.github/workflows/codeql-analysis.yml becomes /home/your-username/your-project/.github/workflows/codeql-analysis.yml

This is based on the implementation in VS Code that is used for the window.title setting. Some of the unit tests are also based on the VS Code unit tests.

This helper function will be used in follow-up PRs that introduce new settings for model packs.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[robertbrignull]

Implementation LGTM. Thanks for including the link to the vscode repo.

Side question: as well as the new model packs uses, do you plan to replace the interpolation in HistoryItemLabelProvider with this implementation?

[koesie10]

Side question: as well as the new model packs uses, do you plan to replace the interpolation in HistoryItemLabelProvider with this implementation?

I don't think we can without breaking existing settings since that uses a format like %q on %d - %s %r [%t] which is incompatible with this "standard" VS Code format. We might be able to deprecate the old format and switch to this new format, but I don't think that's something we're looking into right now.

[charisk]

Side question: as well as the new model packs uses, do you plan to replace the interpolation in HistoryItemLabelProvider with this implementation?

I don't think we can without breaking existing settings since that uses a format like %q on %d - %s %r [%t] which is incompatible with this "standard" VS Code format. We might be able to deprecate the old format and switch to this new format, but I don't think that's something we're looking into right now.

Might be worth an issue to track this as potential tech/product debt.