Dashboard options: windows.*, detent names, positive number types

- dashboard.windowMaxScale / windowDistance -> dashboard.windows.maxScale /
  distance
- windowCurvature: default -> initial, snapPixels/snapPoints ->
  detentPixels/detentPoints, dragThreshold -> dragThresholdPixels (also the
  patch's option keys; window-curvature VERSION 19); removed `snap` now
  points to detentPixels
- types.numbers.positive/nonnegative instead of number + range assertions
  (step <= max, initial/detentPoints <= max and distance min <= max stay)
- frame-controls patch accepts longPressMs from 300, like the option
  (VERSION 2)
- "SteamVR dashboard patch" in descriptions, which fit into 80 columns

Old names keep working with a rename warning.

modules/frame-controls.nix

@@ -1,7 +1,8 @@
 # Move window controls between a dashboard window's bottom bar and its
-# three-dot menu (long press). Dashboard patch (frame-controls/patch.js;
-# "systemui" on 127.0.0.1:8087), registered only when enabled; enables
-# steamvr-debugger.nix (one SteamVR restart the first time).
+# three-dot menu (long press). SteamVR dashboard patch
+# (frame-controls/patch.js; "systemui" on 127.0.0.1:8087), registered only
+# when enabled; enables steamvr-debugger.nix (one SteamVR restart the first
+# time).
 { config, lib, pkgs, ... }:
 let
   cfg = config.steamFrame.dashboard.frameControls;
@@ -25,7 +26,7 @@ in {
       moving SteamVR dashboard window controls between the bottom bar and the
       three-dot menu: long press an icon or menu row for a "Show in bar"
       popup. Applies to that control in all windows, kept across SteamVR
-      restarts. Dashboard patch; off restores stock (next switch)'';
+      restarts. SteamVR dashboard patch; off restores stock (next switch)'';
     longPressMs = mkOption {
       type = types.ints.between 300 10000;
       default = 1500;