This provides indent line like Visual Studio Code's one for
Tree Style Tab's sidebar.
Please note that this requires Tree Style Tab 3.8.5 and later.
Please note that the indent lines won't visible in private windows by default. You need to grant permissions to TST Indent Lines, to access information in private (incognito) windows with two steps:
1) "Add-ons Manager" => "Extensions" => "TST Indent Line" => "Details" => "Run in Private Windows" => "Allow"
2) "Add-ons Manager" => "Extensions" => "Tree Style Tab" => "Options" => "Extra Features via Other Addons" => "Permissions for API Call from Other Addons" => turn on the checkbox in the column "Notify Messages from Private Windows" for the row "tst-indent-line@piro.sakura.ne.jp"
