Disable text file backups when files.autoSave is afterDelay

Part of #16509

Part of #16509

Retain case in workspaces.json paths

Fixes #16829

Addresses #15852 theme problem

Fixes #16879

The recent change assumed that Keybinding.keyCode was the actual keycode but it
is actually the keycode excluding the modifier. This change gets around that by
exposing a Keybinding.isModifierKey function which compares the actual
keybinding against the keybinding with a modifier key binary mask applied.

Fixes #16833

- Show warnings only once
- Open resource editor to show warnings

fixes #16640

fixes #16431

fixes #16625