function asCssVariableName(colorIdent) {
    return `--vscode-${colorIdent.replace(/\./g, '-')}`;
}
Returns the css variable name for the given color identifier. Dots (`.`) are replaced with hyphens (`-`) and
everything is prefixed with `--vscode-`.

@sample `editorSuggestWidget.background` is `--vscode-editorSuggestWidget-background`.